PUBLICACIONES   /   PUBLICATIONS  (David Montes)


PUBLICACIONES INTERNACIONALES

Ca II H & K and Hαemissions in chromospherically active binary systems (RS CVn and BY Dra)

Fernández-Figueroa M.J., Montes D., De Castro E., Cornide M.,

1994, Astrophysical Journal Supplement 90, 433.

ABSTRACT


We report high resolution observations of the Ca II H and K and Balmer Hαlines in 53 chromospherically active binary systems including the RS Canum Venaticorum binaries (RS CVn) and BY Draconis (BY Dra) classes. The rotational periods of the sample cover a range from 0.8 to 83.2 days. H and K emission line surface fluxes have been calculated for all the stars in the sample. In spectra where the Hε line appears in emission, absolute surface fluxes were also determined. The Ca II line profiles corresponding to different seasons and orbital phases are analysed in order to determine the contribution of each component and to study the chromospheric activity variations. We have measured the Hα equivalent width of the program stars and the Hα core emission was determined by subtraction of the equivalent width of a presumably inactive star of the same spectral type and luminosity class. Three different types of Hα line profiles have been found: strong emission line, weak emission line with strong superposed absorption profile, and filled-in absorption line profile.


Citations



The Wilson Bappu effect and other Ca II H and K line parameters relationships in chromospherically active binaries

Montes D., Fernández-Figueroa M.J., De Castro E., Cornide M.,

1994, Astronomy & Astrophysics 285, 609.

ABSTRACT


We present measurements of the emission core width W0 and the wavelength separation of the K1 dips, W1, of the Ca II H and K emission lines observed on high-dispersion spectra of 28 chromospherically active binary systems (RS CVn and BY Dra stars) and 18 single active stars. We test the width-luminosity correlations (the Wilson-Bappu effect, and (W1, MV)) in these very active stars and analyse the influence of the activity level (IK3) and the rotational broadening (Vsin{i}) in these correlations.
We have found that for very active stars the emission widths, both W0 and W1, are larger than expected from previously accepted width-luminosity relations. The stars with strong emission intensities, IK3, and large values of Vsin{i} seem to present larger values of W0 than resulted from WB relation, being the effect of the rotational velocity the most remarkable. On the contrary, W1 is strongly influenced by IK3 but the effect of the rotational broadening is lesser.
We also analyse the behaviour of the Ca~II H and K line parameters in these very active stars in relation with less active stars and we found that the increase of W1 and IK1 with IK3 presents a flattening for the most active stars which is different for each value of W0.
Finally we also find a Hε width-luminosity correlation in the stars of the sample in which this emission line is present.


Citations



Excess Hα emission in chromospherically active binaries

Montes D., Fernández-Figueroa M.J., De Castro E., Cornide M.

1995, Astronomy & Astrophysics 294, 165.

ABSTRACT


We study the behaviour of the excess Hαemission in a sample of 51 chromospherically active binary systems (RS CVn and BY Dra classes), of different activity levels. This sample include the 27 stars analysed by Fernández-Figueroa et al. (1994) and the new observations of 24 systems described by Montes et al. (1994b). By using the spectral subtraction technique (subtraction of a synthesized stellar spectrum constructed from reference stars of similar spectral type and luminosity class) we obtain the active-chromosphere contribution to the Hαline in these 51 systems. We have determined the excess Hαemission equivalent widths and converted it to surface fluxes. The Hα emissions arising from each component star were obtained when it was possible to deblend both contributions. The comparison of the excess Hα emission, obtained with the spectral subtraction technique, with other Hα activity indices allows us to conclude that this is the preferable activity indicator for binaries.
The behaviour of the excess Hα emission as a function of the rotation has been analyzed. A slight decline toward longer rotational periods, P_rot, and larger Rossby numbers, R_0, is present in agreement with previous results using others activity indicators.
We have compared the derived excess Hα emission fluxes with those obtained in the CaII K and Hε lines finding that a good correlation exits between these three chromospheric activity indicators. The Hα losses seem to be more important than CaII K losses for cooler stars, in fact all the system with Hα emission above the continuum are cooler than 5000 K. Correlations with other activity indicators, (CIV in the transition region, and X-rays in the corona) indicate that the exponents of the power-law relations increase with the formation temperature of the spectral features.


Citations



Excess Hα emission in chromospherically active binaries: the spectroscopic survey

Montes D., Fernández-Figueroa M.J., De Castro E., Cornide M.

1995, Astronomy & Astrophysics Suplement 109, 135.

ABSTRACT


We present new spectroscopic Hα observations for a sample of 24 chromospherically active binary systems (RS CVn and BY Dra classes), of different activity levels. By using the spectral subtraction technique (subtraction of a synthesized stellar spectrum constructed from reference stars of similar spectral type and luminosity class) we obtain the active-chromosphere contribution to the Hα line. The Hα emissions arising from each individual star were obtained when it was possible to deblend the contribution of both components.


Citations



Application of the spectral subtraction technique to the Ca II H & K and Hε lines in a sample of chromospherically active binaries

Montes, D., De Castro, E., Fernández-Figueroa, M.J., Cornide, M.

1995, Astronomy & Astrophysics Suplement, (Dec I), 114, 287

ABSTRACT


We present new spectroscopic observations in the Ca II H & K lines region for a sample of 28 chromospherically active binary systems (RS CVn and BY Dra classes), with different activity levels. By using the spectral subtraction technique (subtraction of a synthesized stellar spectrum constructed from reference stars of similar spectral type and luminosity class) we obtain the active-chromosphere contribution to the Ca II H & K lines and to Hε line when it is present. We have compared the emission equivalent widths obtained with this technique with those obtained by reconstruction of the absorption line profile below the emission peak(s).
The emissions arising from each individual star were obtained when it was possible to deblend the contribution of both components. The Ca II line profiles corresponding to different seasons and orbital phases are analysed in order to determine the contribution of each component and to study the chromospheric activity variations.


Citations



The behaviour of the excess Ca II H & K and Hε emissions in chromospherically active binaries

Montes, D., Fernández-Figueroa, M.J., Cornide, M., De Castro, E.,

1996, Astronomy & Astrophysics, (August I), 312, 221

ABSTRACT


In this work we analyze the behaviour of the excess Ca II H & K and Hε emissions in a sample of 73 chromospherically active binary systems (RS CVn and BY Dra classes), of different activity levels and luminosity classes. This sample includes the 53 stars analyzed by Fern\'andez-Figueroa et al. (1994) and the observations of 28 systems described by Montes et al. (1995c). By using the spectral subtraction technique (subtraction of a synthesized stellar spectrum constructed from reference stars of spectral type and luminosity class similar to those of the binary star components) we obtain the active-chromosphere contribution to the Ca II H & K lines in these 73 systems. We have determined the excess Ca II H & K emission equivalent widths and converted them into surface fluxes. The emissions arising from each component were obtained when it was possible to deblend both contributions.

We have found that the components of active binaries are generally stronger emitters than single active stars for a given effective temperature and rotation rate.

A slight decline of the excess Ca II H & K emissions towards longer rotation periods, P_rot, and larger Rossby numbers, R$_{0}$, is found. When we use R$_{0}$ instead of P$_{\rm rot}$ the scatter is reduced and a saturation at R$_{0}$ $\approx$~0.3 is observed.

A good correlation between the excess Ca II K and Hε chromospheric emission fluxes has been found. The correlations obtained between the excess Ca II K emission and other activity indicators, (C IV in the transition region, and X-rays in the corona) indicate that the exponents of the power-law relations increase with the formation temperature of the spectral features.


Citations



Simultaneous Hα, Na I D1, D2, and He I D3 observations of a flare on the RS CVn system UX Ari

Montes, D., Sanz-Forcada, J. Fernández-Figueroa, M.J., Lorente, R.,

1996, Astronomy & Astrophysics, Letter to the Editor, June (III), 310 L29

ABSTRACT


We present simultaneous Hα, NaI D1, D2, and HeI D3 spectroscopic observations on the RS CVn system UX Ari. We have found a dramatic increase in the excess Hα emission equivalent width by a factor of 2 in an interval of 1 day that indicates the beginning of a strong flare in this system. The presence of the HeI D3 in emission in coincidence with the enhancement of the Hα emission confirms the detection of a flare. The application of the spectral subtraction technique reveals that the core of the NaI D1 and D2 lines are also filled-in by chromospheric emission.


Citations



Hα emission fluxes and lithium abundances of low mass stars in the young open cluster IC4665

Martín E.L., Montes, D. -- (accepted May 1996)

1997, Astronomy & Astrophysics (Feb. III) 318, 805

ABSTRACT


As part of a long term effort to understand pre-main sequence Li burning, we have obtained high resolution spectroscopic observations of 14 late type stars (G0-M1) in the young open cluster IC 4665. Most of the stars have Hα filled-in and Li absorption, as expected for their young age. From the equivalent widths of Hα emission excess (obtained using the spectral subtraction technique) and the LiI feature, we have derived Hα emission fluxes and photospheric Li abundances. The mean Li abundance of IC~4665 solar-type stars is log N(Li)=3.1; the same as in other young clusters (alpha Per, Pleiades) and T Tauri stars. Our results support the conclusions from previous works that PMS Li depletion is very small for masses ~1 M_sun. Among the IC 4665 late-G and early K-type stars, there is a spread in Li abundances of about one order of magnitude. The Li-poor IC 4665 members have low Hα excess and vsini <10. Hence, the Li-activity-rotation connection which has been clearly established in the Pleiades also seems to hold in IC 4665. One M-type IC 4665 star that we have observed does not show Li, implying a very efficient Li depletion as observed in alpha Per stars of the same spectral type. The level of chromospheric activity and Li depletion among the low mass stars of IC 4665 is similar to that in the Pleiades. In fact, we note that the Li abundance distributions in several young clusters (alpha Per, Pleiades, IC 2391, IC 4665) and in post T Tauri stars are strikingly similar. This result suggests that \ha emission and Li abundance not well correlated with age for low mass stars between 20 and 100 Myr old. We argue that a finer age indicator, the ``LL-clock", would be the luminosity at which the transition between efficient Li depletion and preservation takes place for fully convective objects. The LL-clock could allow in the near future to derive the relative ages of young open clusters, and clarify the study of PMS evolution of cool stars.


Citations



Library of high and mid-resolution spectra in the CaII H & K, Hα, Hβ, and NaI D1, D2, and HeI D3 line regions of F, G, K and M field stars

Montes D., Martín E.L., Fernández-Figueroa M.J., Cornide M., De Castro E., (accepted September 1996)

1997, Astronomy & Astrophysics Supp. S. (June II), 123, 473

ABSTRACT


In this work we present spectroscopic observations centered in the spectral lines most widely used as optical indicators of chromospheric activity (Hα, Hβ, CaII H & K, and and HeI D3) in a sample of F, G, K and M chromospherically inactive stars. The spectra have been obtained with the aim of providing a library of high and mid-resolution spectra to be used in the application of the spectral subtraction technique to obtain the active-chromosphere contribution to these lines in chromospherically active single and binary stars. This library can also be used for spectral classification purposes. A digital version with all the spectra is available via ftp and the World Wide Web (WWW).


Citations



Multiwavelength optical observations of chromospherically active binary systems.
I. Simultaneous Hα, NaI D1, D2, and HeI D3 observations

Montes D., Fernández-Figueroa M.J., De Castro E., Sanz-Forcada J., (accepted December 1996)

1997, Astronomy & Astrophysics Supp. S., (Oct II), 125, 263

ABSTRACT


This is the first paper of a series aimed at studying the chromosphere of active binary systems using the information provided for several optical spectroscopic features. Simultaneous Hα, NaI D1, D2, and HeI D3 spectroscopic observations are reported here for 18 systems. The chromospheric contribution in these lines have been determined using the spectral subtraction technique. Very broad wings have been found in the subtracted Hα profile of some of the more active stars. These profiles are well matched using a two-components Gaussian fit (narrow and broad) and the broad component could be interpreted as arising from microflaring. Prominence-like extended material have been detected in a near-eclipse Hα observation of the system AR Lac. The excess emission found in the NaI D1 and D2 lines by application of the spectral subtraction technique and the behaviour of the Hα line in the corresponding simultaneous observations indicate that the filling-in of the core of these lines is a chromospheric activity indicator. For giant stars of the sample the HeI D3 line has been detected in absorption in the subtracted spectra. An optical flare has been detected in UX Ari and II Peg through the presence of the HeI D3 in emission in coincidence with the enhancement of the Hα emission.


Citations



Multiwavelength optical observations of chromospherically active binary systems.
II. EZ Pegasi

Montes D., Sanz-Forcada J., Fernández-Figueroa M.J., De Castro E., Poncet A. (accepted July 1997)

1998, Astronomy & Astrophysics, (Feb I), 330, 155

ABSTRACT


The star EZ Peg, long ago classified as cataclysmic variable, has been shown to be a chromospherically active binary system of the RS CVn-type. In this paper we have analysed, using the spectral subtraction technique, simultaneous spectroscopic observations of the Hα, Hβ, NaI D1, D2, HeI D3, MgI b triplet, CaII H & K, and CaII infrared triplet lines. We have found that the hot component is the active star of he system, showing strong emission in the Hα, CaII H & K, Hε, and CaII IRT λ8498 and λ8662 lines, and a filling-in of the Hβ line. The variations (in time and with the orbital phase) observed in the different indicators, formed at different height in the chromosphere, are correlated. Very broad wings have been found in the subtracted profiles of Hα and CaII IRT λ8498 and λ8662 lines. These profiles are well matched using a two-components Gaussian fit (narrow and broad) and the broad component could be interpreted as arising from microflaring. The higher luminosity class of the hot component, that our spectra seem to indicate, could explain why the hot component is the active star of the system.


Citations



Library of high-resolution UES echelle spectra of F, G, K and M field dwarf stars

Montes D., Martín E.L., (accepted August 1997)

1998, Astronomy & Astrophysics Supp. S. (Mar II), 128, 485

ABSTRACT


We present a library of Utrecht echelle spectrograph (UES) observations of a sample of F, G, K and M field dwarf stars covering the spectral range from 4800 AA to 10600 AA with a resolution of 55000. These spectra include some of the spectral lines most widely used as optical and near-infrared indicators of chromospheric activity such as Hβ, Mg I b triplet, NaI D1,D2, HeI D3, Hα, and Ca II IRT lines, as well as a large number of photospheric lines which can also be affected by chromospheric activity. The spectra have been compiled with the aim of providing a set of standards observed at high-resolution to be used in the application of the spectral subtraction technique to obtain the active-chromosphere contribution to these lines in chromospherically active single and binary stars. This library can also be used for spectral classification purposes. A digital version with all the spectra is available via ftp and the World Wide Web (WWW) in both ASCII and FITS formats.


Citations



Detection of Li I enhancement during a long-duration stellar flare

Montes D., Ramsey L.W., (accepted October 1998)

1998, Astronomy and Astrophysics, Letter to the Editor, (Dec I), 340, L5

ABSTRACT


We report the detection of a LiI λ6708 Å line enhancement during an unusual long-duration optical flare in the recenltly discovered, X-ray/EUV selected, chromospherically binary 2RE~J0743+224. The LiI equivalength width (EW) variations follows the temporal evolution of the flare and large changes are observed in the intensity of the line. The maximum LiI enhancement (40% in EW) occurs just after the maximum chromospheric emission observed in the flare. A significant increase of the $^6$Li/$^7$Li isotopic ratio is also detected. No siginificant variations are detected in other photospheric lines. Neither line blends nor starspots seem to be the primary cause of the observed LiI line variation. From all this we suggest that this LiI enhancement is produced by spallation reactions during the flare. This is the first time that such LiI enhancement associate with a stellar flare is reported, and probably the long-duration of this flare is a key factor for this detection.


Citations



Optical and UV observations of a strong flare in the young, single K2-dwarf LQ Hya

D. Montes, S.H. Saar, A. Collier Cameron, Y.C. Unruh

1999, MNRAS 305 (Number 1, 1 May), 45

ABSTRACT


We present high resolution optical echelle spectra and IUE observations during a strong flare on 1993 December 22 in the very active, young, rapidly rotating, single K2 dwarf LQ Hya. The initial impulsive phase of the flare, which started sometime between 2:42 UT and 4:07 UT, was characterized by strong optical continuum enhancement and blue-shifted emission lines with broad wings. The optical chromospheric lines reached their maximum intensity at $\approx$5:31 UT, by which time the blue-shift vanished and the optical continuum enhancement had sharply decreased. Thereafter, the line emission slowly decreased and the lines red-shift in a gradual phase that lasted at least two more hours. The Mg II lines behaved similarly. Quiescent C IV flux levels were not recovered until 21 hours later, though a data gap and a possible second flare make the interpretation uncertain. In addition to the typically flare-enhanced emission lines (e.g., Hα and Hβ), we observe He I D_3 going into emission, plus excess emission (after subtraction of the quiescent spectrum) in other He I and several strong neutral metal lines (e.g., Mg I b). Flare enhancement of the far UV continuum generally agrees with a Si I recombination model. We estimate the total flare energy, and discuss the broad components, asymmetries, and Doppler shifts seen in some of the emission lines.


Citations



Library of medium-resolution Fiber Optic Echelle spectra of
F, G, K and M field dwarfs to giants stars

D. Montes, L.W. Ramsey, A.D. Welty (accepted November 1998)

1999, Astrophysical Journal Supplement Series, 123, 283 (July 1999 Vol. 123 #1)

ABSTRACT


We present here a library of Penn State Fiber Optic Echelle (FOE) observations of a sample of field stars with spectral types F to M and luminosity classes V to I. The spectral coverage is from 3800 AA to 10000 AA with nominal resolution 12000. These spectra include many of the spectral lines most widely used as optical and near-infrared indicators of chromospheric activity such as the Balmer lines (Hα to Hε), Ca II H & K, Mg I b triplet, Na I D1,D2, He I D3, and Ca II IRT lines, as well as a large number of photospheric lines, which can also be affected by chromospheric activity, and temperature sensitive photospheric features such as TiO bands. The spectra have been compiled with the aim of providing a set of standards observed at medium-resolution. We have extensively used such data for the study of active chromosphere stars by applying a spectral subtraction technique. However, the data set presented here can also be utilized in a wide variety of ways ranging from radial velocity templates to study of variable stars and stellar population synthesis. This library can also be used for spectral classification purposes, and determination of atmospheric parameters (T_eff}, log{g}, [Fe/H]). A digital version with all the fully reduced spectra is available via ftp and the World Wide Web (WWW) in FITS format.


Citations



Multiwavelength optical observations of chromospherically active binary systems.
III. High resolution echelle spectra from Ca II H&K to Ca II IRT

Montes D., M.J. Fernández-Figueroa, E. De Castro M. Cornide, A. Latorre, J. Sanz-Forcada,

2000, Astronomy & Astrophysics Supp. S., 146, 103

ABSTRACT


This is the third paper of a series aimed at studying the chromosphere of active binary systems using the information provided for several optical spectroscopic features. High resolution echelle spectra including all the optical chromospheric activity indicators from the Ca II H & K to Ca II IRT lines are analysed here for 16 systems. The chromospheric contribution in these lines has been determined using the spectral subtraction technique.
Very broad wings have been found in the subtracted Hα profile of the very active star HU Vir. These profiles are well matched using a two-component Gaussian fit (narrow and broad) and the broad component can be interpreted as arising from microflaring.
Red-shifted absorption features in the Hα line have been detected in several systems and excess emission in the blue wing of FG UMa was also detected. These features indicate that several dynamical processes, or a combination of them, may be involved.
Using the E(Hα)/E(Hβ) ratio as a diagnostic we have detected prominence-like extended material viewed off the limb in many stars of the sample, and prominences viewed against the disk at some orbital phases in the dwarfs OU Gem and BF Lyn.
The He I D_3 line has been detected as an absorption feature in mainly all the giants of the sample. Total filling-in of the He I D_3, probably due to microflaring activity, is observed in HU Vir.
Self-absorption with red asymmetry is detected in the Ca II H & K lines of the giants 12 Cam, FG UMa and BM CVn.
All the stars analysed show clear filled-in Ca II IRT lines or even notable emission reversal. The small values of the E(8542)/E(8498) ratio we have found indicate Ca II IRT emission arises from plage-like regions.
Orbital phase modulation of the chromospheric emission has been detected in some systems, in the case of HU Vir evidence of an active longitude area has been found.


Citations



Late-type stars members of young stellar kinematic groups. I. Single stars

Montes D., López-Santiago J., Gálvez M.C., Fernández-Figueroa M.J., De Castro E., Cornide M.,

2001, Monthly Notices of the Royal Astronomical Society, MNRAS 328, 45

ABSTRACT


This is the first paper of a series aimed at studying the properties of late-type stars members of young stellar kinematic groups. We center our study in classical young moving groups as: Local Association (Pleiades moving group, 20 - 150 Myr), IC 2391 supercluster (35 Myr), Ursa Major group (Sirius supercluster, 300 Myr), and Hyades supercluster (600 Myr); as well as in recently identified groups as: Castor moving group (200 Myr).
In this paper we have compiled a preliminary list of single late-type stars possible members of some of these young stellar kinematic groups. Stars have been selected from previously established members of stellar kinematic groups based in photometric and kinematic properties as well as from candidates based in other criteria as their level of chromospheric activity, rotation rate, lithium abundance. Precise measurements of proper motions and parallaxes taken from Hipparcos Catalogue, as well as from Tycho-2 Catalogue, and published radial velocity measurements are used to calculate Galactic space motions (U, V, W) and apply the Eggen's kinematic criteria in order to determine the membership of the selected stars to the different groups. Additional criteria using age-dating methods for late-type stars will be applied in forthcoming papers of this series.
A further study of the list of stars compiled here could lead to a better understanding of the chromospheric activity and their age evolution as well as of the star formation history in the solar neighbourhood. In addition, these stars are also potential search targets for direct imaging detection of sub-stellar companions


Citations



Chromospheric activity, lithium and radial velocities of single late-type stars possible members of young moving groups

Montes D., López-Santiago J., Fernández-Figueroa M.J., Gálvez M.C.,

2001, Astronomy & Astrophysics, A&A 379, 976

ABSTRACT


We present here high resolution echelle spectra taken during three observing runs of 14 single late-type stars identified in our previous studies (Montes et al. 2001b, hereafter Paper I) as possible members of different young stellar kinematic groups (Local Association (20 - 150 Myr), Ursa Major group (300 Myr), Hyades supercluster (600 Myr), and IC 2391 supercluster (35 Myr)). Radial velocities have been determined by cross correlation with radial velocity standard stars and used together with precise measurements of proper motions and parallaxes taken from Hipparcos and Tycho-2 Catalogues, to calculate Galactic space motions (U, V, W) and to apply Eggen's kinematic criteria. The chromospheric activity level of these stars have been analysed using the information provided for several optical spectroscopic features (from the Ca II H & K to Ca II IRT lines) that are formed at different heights in the chromosphere. The Li I 6707.8 Å line equivalent width (EW) has been determined and compared in the EW(Li I) versus spectral type diagram with the EW(Li I) of stars members of well known young open clusters of different ages, in order to obtain an age estimation. All these data allow us to analyse in more detail the membership of these stars in the different young stellar kinematic groups. Using both kinematic and spectroscopic criteria we have confirmed PW And, V368 Cep, V383 Lac, EP Eri, DX Leo, HD 77407, and EK Dra as members of the Local Association and V834 Tau, pi^{1} UMa, and GJ 503.2 as members of the Ursa Major group. A clear rotation-activity dependence has been found in these stars.


Citations



Multiwavelength optical observations of chromospherically active binary systems.
IV. The X-ray/EUV selected binary BK Psc (2REJ 0039+103)

Gálvez M.C., Montes D., Fernández-Figueroa M.J., López-Santiago J., De Castro E., Cornide M.,

2002, Astronomy & Astrophysics 389, 524

ABSTRACT


We present high resolution echelle spectra taken during four observing runs from 1999 to 2001 of the recently, X-ray/EUV selected chromospherically active binary BK Psc (2RE J0039+103). Our observations confirm the single-lined spectroscopic binary (SB1) nature of this system and allow us to obtain, for the first time, the orbital solution of the system as in the case of a SB2 system. We have determined precise radial velocities of both components: for the primary by using the cross correlation technique, and for the secondary by using its chromospheric emission lines. We have obtained a near circular orbit with an orbital period of 2.1663 days, very close to its photometric period of 2.24 days (indicating synchronous rotation). The spectral type (K5V) we determined for our spectra and the mass ratio (1.8) and minimum masses (Msin^3i) resulting from the orbital solution are compatible with the observed K5V primary and an unseen M3V secondary. Using this spectral classification, the projected rotational velocity (vsini, of 17.1 km s-1) obtained from the width of the cross-correlation function, and the data provided by Hipparcos we have derived other fundamental stellar parameters. The kinematics and the non- detection of the Li I indicate that it is an old star. The analysis of the optical chromospheric activity indicators from the Ca II H & K to Ca II IRT lines, by using the spectral subtraction technique, indicates that both components of the binary system show high levels of chromospheric activity. Ha emission above the continuum from both components is a persistent feature of this system during the period 1999 to 2001 of our observations as well as in previous observations. The Ha and Hb emission seems to arise from prominence-like material, and the Ca II IRT emission from plage-like regions.


Citations



Simultaneous Optical and X-ray Observations of Flares and Rotational Modulation on the RS CVn Binary HR 1099 (V711 Tau) from the MUSICOS 1998 Campaign

García-Alvarez D., Foing B., Montes D., Oliveira J., Doyle J.G., and MUSICOS 1998 Collaboration

2003, Astronomy & Astrophysics, A&A 397, 285

ABSTRACT


We present simultaneous and continuous observations of the Ha, Hb, HeI D3, NaI D1,D2 doublet and the CaII H&K lines for the RS CVn system HR 1099. The spectroscopic observations were obtained during the MUSICOS 1998 campaign involving several observatories and instruments, both echelle and long-slit spectrographs. During this campaign, HR 1099 was observed almost continuously for more than 8 orbits of 2.8 days. Two large optical flares were observed, both showing an increase in the emission of Ha, CaII H & K, Hb and HeI D3 and a strong filling-in of the NaI D1,D2 doublet. Contemporary photometric observations were carried out with the robotic telescopes APT-80 of Catania and Phoenix-25 of Fairborn Observatories. Maps of the distribution of the spotted regions on the photosphere of the binary components were derived using the Maximum Entropy and Tikhonov photometric regularization criteria. Rotational modulation was observed in Ha and HeI D3 in anti-correlation with the photometric light curves. Both flares occurred at the same binary phase (0.85), suggesting that these events took place in the same active region. Simultaneous X-ray observations, performed by ASM on board RXTE, show several flare-like events, some of which correlate well with the observed optical flares. Rotational modulation in the X-ray light curve has been detected with minimum flux when the less active G5V star was in front. A periodicity in the X-ray flare-like events was also found.


Citations



Rotational modulation of the photospheric and chrosmospheric activity in the young, single K2-dwarf PW And

López-Santiago J., Montes D., Fernández-Figueroa M.J., Ramsey L.W.,

2003, Astronomy & Astrophysics, A&A, 411, 489

ABSTRACT


High resolution echelle spectra of PW And (HD 1405) have been taken during eight observing runs from 1999 to 2002. The detailed analysis of the spectra allow us to determine its spectral type (K2V), mean heliocentric radial velocity (V_hel = -11.15 km/s) rotational velocity (vsin{i} = 22.6 km/s), and equivalent width of the lithium line 6707.8 Å (EW(LiI) = 273 mÅ). The kinematic (Galactic Velocity (U, V, W)) confirms its membership of the Local Association moving group, in agreement with the age (30 to 80 Myrs) inferred from the color magnitude diagram and the lithium equivalent width. Photospheric activity (presence of cool spots that disturb the profiles of the photospheric lines) has been detected as changes in the the bisectors of the cross correlation function (CCF) resulting of cross-correlate the spectra of PW And with the spectrum of a non active star of similar spectral type. These variations of the CCF bisectors are related to the variations in the measured radial velocities and are modulated with a period similar to the photometric period of the star. At the same time, chromospheric activity has been analyzed, using the spectral subtraction technique and simultaneous spectroscopic observations of the Hα, Hβ, NaI D_1 and D_2, HeI D_3, MgI b triplet, CaII H&K, and CaII infrared triplet lines. A flare was observed during the last observing run of 2001, showing an enhancement in the observed chromospheric lines. A less powerful flare was observed on 2002 August 23. The variations of the chromospheric activity indicators seem to be related to the photospheric activity. A correlation between radial velocity, changes in the CCF bisectors and equivalent width of different chromospheric lines is observed with a different behaviour between epochs 1999, 2001 and 2002.


Citations



The nearest young moving groups

López-Santiago J., Montes D., Crespo-Chacón I., Fernández-Figueroa M.J.,

2006, Astrophysical Journal, ApJ, 643, 1160

ABSTRACT


The latest results in the research of forming planetary systems have led several authors to compile a sample of candidates for searching for planets in the vicinity of the sun. The young stellar associations are indeed excellent laboratories for this study, but some of them are not close enough to allow the detection of planets through adaptive optics techniques. However, the existence of very close young moving groups can solve this problem. Here we have compiled the members of the nearest young moving groups, as well as a list of new candidates from our study of late-type stars possible members of young stellar kinematic groups, studying their membership using spectroscopic and photometric criteria.


Citations



Analysis and modelling of high temporal resolution spectroscopic observations of flares on AD Leo

Crespo-Chacón I., Montes D., García-Álvarez D, Fernández-Figueroa M.J., López-Santiago J., Foing B.H.,

2006, Astronomy & Astrophysics, A&A, 452, 987

ABSTRACT


We report the results of a high temporal resolution spectroscopic monitoring of the flare star AD Leo. During 4 nights, more than 600 spectra were taken in the optical range using the Isaac Newton Telescope (INT) and the Intermediate Dispersion Spectrograph (IDS). We have observed a large number of short and weak flares occurring very frequently (flare activity > 0.71 hours-1). This is in favour of the very important role that flares can play in stellar coronal heating. The detected flares are non white-light flares and, though most of solar flares belong to this kind, very few such events had been previously observed on stars. The behaviour of different chromospheric lines (Balmer series from Hα to H_11, Ca II H & K, Na I D_1 & D_2, He I 4026 AA and He I D_3) has been studied in detail for a total of 14 flares. We have also estimated the physical parameters of the flaring plasma by using a procedure which assumes a simplified slab model of flares. All the obtained physical parameters are consistent with previously derived values for stellar flares, and the areas - less than 2.3% of the stellar surface - are comparable with the size inferred for other solar and stellar flares. Finally, we have studied the relationships between the physical parameters and the area, duration, maximum flux and energy released during the detected flares.


Citations



The First Extrasolar Planet Discovered with a New Generation High Throughput Doppler Instrument [ET-1, HD 102195 b]

J. Ge, J. van Eyken, S. Mahadevan, C. DeWitt, S.R. Kane, R. Cohen, A. Vanden Heuvel, S.W. Fleming, P. Guo, G.W. Henry, D.P. Schneider, L.W. Ramsey, R.A. Wittenmyer, M. Endl, W.D. Cochran, E.B. Ford, E.L. Martín, G. Israelian, J. Valenti, D. Montes,

2006, Astrophysical Journal, ApJ, 648, 683

ABSTRACT


We report the detection of the first extrasolar planet, ET-1 (HD 102195b), using the Exoplanet Tracker (ET), a new generation Doppler instrument. The planet orbits HD 102195, a young star with solar metallicity that may be part of the local association. The planet imparts radial velocity variability to the star with a semiamplitude of 63.4 ± 2.0 m s-1 and a period of 4.11 days. The planetary minimum mass (msin i) is 0.488 ± 0.015 MJ . The planet was initially detected in the spring of 2005 with the Kitt Peak National Observatory (KPNO) 0.9 m coudé feed telescope. The detection was confirmed by radial velocity observations with the ET at the KPNO 2.1 m telescope and also at the 9 m Hobby-Eberly Telescope (HET) with its High Resolution Spectrograph. This planetary discovery with a 0.9 m telescope around a V = 8.05 magnitude star was made possible by the high throughput of the instrument: 49% measured from the fiber output to the detector. The ET’s interferometer-based approach is an effective method for planet detection. In addition, the ET concept is adaptable to multiple-object Doppler observations or very high precision observations with a cross-dispersed echelle spectrograph to separate stellar fringes over a broad wavelength band. In addition to spectroscopic observations of HD 102195, we obtained brightness measurements with one of the automated photometric telescopes (APTs) at Fairborn Observatory. Those observations reveal that HD 102195 is a spotted variable star with an amplitude of ~0.015 mag and a 12.3 ± 0.3 day period. This is consistent with spectroscopically observed Ca II H and K emission levels and line broadening measurements but inconsistent with rotational modulation of surface activity as the cause of the radial velocity variability. Our photometric observations rule out transits of the planetary companion.


Citations



Multiwavelength optical observations of chromospherically active binary systems.
V. FF UMa (2RE J0933+624): a system with orbital period variation

Gálvez M.C., Montes D., Fernández-Figueroa M.J., De Castro E., Cornide M.,

2007, Astronomy & Astrophysics, A&A, 472, 587

ABSTRACT


This is the fifth paper in a series aimed at studying the chromospheres of active binary systems using several optical spectroscopic indicators to obtain or improve orbital solution and fundamental stellar parameters. We present here the study of FF UMa (2RE J0933+624), a recently discovered, X-ray/EUV selected, active binary with strong Hα emission. The objectives of this work are, to find orbital solutions and define stellar parameters from precise radial velocities and carry out an extensive study of the optical indicators of chromospheric activity. We obtained high resolution echelle spectroscopic observations during five observing runs from 1998 to 2004. We found radial velocities by cross correlation with radial velocity standard stars to achieve the best orbital solution. We also measured rotational velocity by cross-correlation techniques and have studied the kinematic by galactic space-velocity components (U, V, W) and Eggen criteria. Finally, we have determined the chromospheric contribution in optical spectroscopic indicators, from Ca II H & K to Ca II IRT lines, using the spectral subtraction technique. We have found that this system presents an orbital period variation, higher than previously detected in other RS CVn systems. We determined an improved orbital solution, finding a circular orbit with a period of 3.274 days. We derived the stellar parameters, confirming the subgiant nature of the primary component (M_P = 1.67 M_Sun and Rsini_P = 2.17 R_Sun) and obtained rotational velocities (vsini), of 33.57+-0.45 km/s and 32.38+-0.75 km/s for the primary and secondary components respectively. From our kinematic study, we can deduce its membership to the Castor moving group. Finally, the activity study has given us a better understanding of the possible mechanism that produce the orbital period variation.


Low-resolution spectroscopy and spectral energy distributions of selected sources towards σ Orionis

Caballero J.A., Valdivielso L., Martín E.L., Montes D., Pascual S., Pérez-González P.G.,

2008, Astronomy & Astrophysics, A&A, 491, 515

ABSTRACT


Aims. We study in detail nine sources in the direction of the young σ Orionis cluster, which is considered to be a unique site for studying stellar and substellar formation. The nine sources were selected because of their peculiar properties, such as extremely-red infrared colours or excessively strong Hα emission for their blue optical colours.
Methods. We acquired high-quality, low-resolution spectroscopy (R 500) of the nine targets with ALFOSC at the Nordic Optical Telescope. We also re-analysed [24]-band photometry from MIPS/Spitzer and compiled the highest quality photometric dataset available at the ViJHKs passbands and the four IRAC/Spitzer channels, for constructing accurate spectral energy distributions between 0.55 and 24 μm.
Results. The nine targets were classified into: one Herbig Ae/Be star with a scattering edge-on disc; two G-type stars; one X-ray flaring, early-M, young star with chromospheric Hα emission; one very low-mass, accreting, young spectroscopic binary; two young objects at the brown-dwarf boundary with the characteristics of classical T Tauri stars; and two emission-line galaxies, one undergoing star formation, and another whose spectral energy distribution is dominated by an active galactic nucleus. We also discovered three infrared sources associated with overdensities in a cold cloud of the cluster centre.
Conclusions. Low-resolution spectroscopy and spectral energy distributions are a vital tool for measuring the physical properties and evolution of young stars and candidates in the σ Orionis cluster.


Multiwavelength optical observations of two chromospherically active binary systems: V789 Mon and GZ Leo

Gálvez M.C., Montes D., Fernández-Figueroa M.J., De Castro E., Cornide M.,

2009, Astronomical Journal, AJ, 137, 3965

ABSTRACT


This paper describes a multiwavelengh optical study of chromospheres in two X-ray/EUV selected active binary stars with strong Hα emission, V789 Mon (2RE J0725-002) and GZ Leo (2RE J1101+223). The goal of the study is to determine radial velocities and fundamental stellar parameters in chromospherically active binary systems in order to include them in the activity-rotation and activity-age relations. We carried out high resolution echelle spectroscopic observations and applied spectral subtraction technique in order to measure emission excesses due to chromosphere. The detailed study of activity indicators allowed us to characterize the presence of different chromospheric features in these systems and enabled to include them in a larger activity-rotation survey. We computed radial velocities of the systems using cross correlation with the radial velocity standards. The double-line spectral binarity was confirmed and the orbital solutions improved for both systems. In addition, other stellar parameters such as: spectral types, projected rotational velocities (vsini), and the equivalent width of the lithium LiI λ6707.8 Å absorption line were determined.


Quantifying the contamination by old main-sequence stars in young moving groups: the case of the Local Association.

López-Santiago J., Micela G., Montes D.,

2009, Astronomy & Astrophysics, A&A, 499, 129

ABSTRACT


Context. The associations and moving groups of young stars are excellent laboratories to investigate the stellar formation in the solar neighborhood. Previous results confirmed that a non-negligible fraction of old main-sequence stars is present in the lists of possible members of the young stellar kinematic groups. A detailed study on the properties of these samples is needed to separate the young stars from old main-sequence stars with similar space motion, in order to identify the origin of these structures.
Aims. Our intention is to characterize members of the young moving groups, determine their age distribution, and quantify the contamination by old main-sequence stars, in particular, for the Local Association.
Methods. We used stars possible members of the young (~10 - 650 Myr) moving groups from the literature. To determine the age of the stars, we used several suitable age indicators for young main sequence stars, i.e., X-ray fluxes from the Rosat All-sky Survey database, photometric data from the Tycho-2, Hipparcos, and 2MASS database. We also used spectroscopic data, in particular the equivalent width of the lithium line Li I λ6707.8 Å and Hα, to constrain the range of ages of the stars.
Results. By combining photometric and spectroscopic data, we were able to separate the young stars (10 - 650 Myr) from the old (> 1 Gyr) field ones. We found, in particular, that the Local Association is contaminated by old field stars at the level of ~30% . This value must be considered as the contamination for our particular sample, and not of the entire Local Association. For other young moving groups, it is more difficult to estimate the fraction of old stars among possible members. However, the level of X-ray emission can, at least, help to separate two age populations: stars with < 200 Myr and stars older than this.
Conclusions. Among the candidate members of the classical moving groups, there is a non-negligible fraction of old field stars that should be taken into account when studying the stellar birthrate in the solar neighborhood. Our results are consistent with a scenario in which the moving groups contain both groups of young stars formed in a recent star-formation episode and old field stars with similar space motion. Only by combining X-ray and optical spectroscopic data is it possible to distinguish between these two age populations.


Chromospheric activity and rotation of FGK stars in the solar vicinity. An estimation of the radial velocity jitter

Martínez-Arnáiz R.M., Maldonado J., Montes D., Eiroa C., Montesinos M.,

2010, Astronomy & Astrophysics, A&A, 520, A79

ABSTRACT


Context. Chromospheric activity produces both photometric and spectroscopic variations that can be mistaken as planets. Large spots crossing the stellar disc can produce planet-like periodic variations in the light curve of a star. Moreover, spots clearly affect the spectral line profiles. Such perturbations will in turn affect the line centroids creating a radial velocity jitter that might “contaminate” the variations induced by a planet. Precise chromospheric activity measurements are needed to estimate the activity-induced noise that should be expected for a given star.
Aims. The purpose of this paper is to obtain precise chromospheric activity measurements and projected rotational velocities for nearby (d < 25 pc) cool (spectral types F to K) stars, in order to estimate the activity-related jitter that should be expected for them. As a complementary objective, in this paper we aim to obtain relationships between fluxes in different activity indicator lines, which will permit a transformation of traditional activity indicators, i.e, Ca II H & K lines, to other which hold noteworthy advantages.
Methods. We used high resolution ( 50000) echelle optical spectra. Standard data reduction was performed using the IRAF ECHELLE package. To reveal the chromospheric emission of the stars in the sample we used the spectral subtraction technique. We measured equivalent widths of the chromospheric emission lines in the subtracted spectrum and transformed them into fluxes by applying empirical equivalent width-flux relationships. Rotational velocities were determined using the cross-correlation technique. To infer activity-related radial velocity (RV) jitter we used empirical relationships between this and the R'_HK index.
Results. We have measured chromospheric activity, as given by different indicators throughout the optical spectra, and projected ro- tational velocities for 371 nearby cool stars. We have built empirical relationships among the most important chromospheric emission lines. Finally, we have used the measured chromospheric activity to estimate the expected RV jitter for the active stars in the sample.


A high-resolution spectroscopic survey of late-type stars: chromospheric activity, rotation, kinematics, and age.

López-Santiago J., Montes D., Gálvez-Ortiz M.C., Crespo-Chacón I., Martínez-Arnáiz R.M., Fernández-Figueroa M.J., De Castro E., Cornide M.,

2010, Astronomy & Astrophysics, A&A, 514, A97

ABSTRACT


Aims. We present a compilation of spectroscopic data from a survey of 144 chromospherically active young stars in the solar neighborhood which may be used to investigate different aspects of the formation and evolution of the solar neighborhood in terms of kinematics and stellar formation history. The data have already been used by us in several studies. With this paper, we make all these data accessible to the scientific community for future studies on different topics.
Methods. We performed spectroscopic observations with echelle spectrographs to cover the entirety of the optical spectral range simultaneously. Standard data reduction was performed with the IRAF echelle package. We applied the spectral subtraction technique to reveal chromospheric emission in the stars of the sample. The equivalent width of chromospheric emission lines was measured in the subtracted spectra and then converted to fluxes using equivalent width--flux relationships. Radial and rotational velocities were determined by the cross-correlation technique. Kinematics, equivalent widths of the lithium line λ6707.8 Å and spectral types were also determined.
Results. A catalog of spectroscopic data is compiled: radial and rotational velocities, space motion, equivalent widths of optical chromospheric activity indicators from Ca II H&K to the calcium infrared triplet and the lithium line in λ6708 Å. Fluxes in the chromospheric emission lines and R'_HK are also determined for each observation of star in the sample. We used these data to investigate the emission levels of our stars. The study of the Hα emission line revealed the presence of two different populations of chromospheric emitters in the sample, clearly separated in the logF_Hα/F_bol - (V-J) diagram. The dichotomy may be associated with the age of the stars.


Late-type stars members of young stellar kinematic groups. II. Chromospherically active binaries

Montes D., Gálvez M.C., López-Santiago J., Fernández-Figueroa M.J., Cornide M., De Castro E.,

2010, MNRAS (in preparation)

ABSTRACT
















OTRAS PUBLICACIONES


Emisión Cromoférica Hα en sistemas binarios RS CVn

Montes D., Fernández-Figueroa M.J.,

1991, Proceedings de la XVIII Reunión Bienal de la Real Sociedad Española de Física, Libro de Resumenes Tomo II, 20. OR-11.

ABSTRACT



Emisión Hα en sistema binarios cromosféricamente activos (RS CVn y BY Dra)

Fernández-Figueroa M.J., Montes D., De Castro E.

1992, Anales de Física 88, 39.

ABSTRACT


We report here high and medium resolution Balmer Hα line profiles for 11 chromospherically active binary systems including the class of RS Canum Venaticorum binaries (RS CVn) and BY Draconis (BY Dra) with a total range of rotation periods from 0.8 to 24 days. We have obtained different types of Hα line profiles: strong emission line, weak emission line with strong superposed absorption profile and filled-in absorption line profile. We have measured the Hα equivalent width of the program stars and the Hα core emission was determined by subtraction of the equivalent width of a presumably inactive star with the same spectral type and luminosity class.


Analysis of Chromospheric Activity Indicators in MM Her and AR Psc

Montes D., De Castro E., Cornide M., Fernández-Figueroa M.J.,

1993, Physics of Solar and Stellar Coronae, Kluwer Academic Publishers, J.L. Linsky and S. Serio (eds.), p. 475.

ABSTRACT


High resolution observations of Hα and Ca II H and K have been carried out at Calar Alto and Roque de Los Muchachos Observatories. The H and K observations at two different phases of MM Her has allowed us to derived that the two components are chromospherically active being the activity level of the cool component much higher. On the contrary AR Psc shows H and K emission from only one component at all the orbital phases, this star presents also an important Hε emission. The Hα observations confirm the different chromospheric behaviour above mentioned.


Spectroscopic study of five chromospherically active binaries with the Hα line in emission

Montes D., De Castro E., Cornide M., Fernández-Figueroa M.J.,

1994, Cool Stars, Stellar Systems, and the Sun Eighth Cambridge Workshop, J.P. Caillault (ed.) ASP Conference Series 64, 444.

ABSTRACT


We report high resolution observations of Hαand the Ca~II H and K lines in five chromospherically active binaries, which present the Hαline in emission above the continuum. Hαequivalent widths (EW) have been determined and Ca~II H and K surface fluxes have been calculated.


Citations



Exceso de emisión Hβ en sistemas binarios con actividad cromosférica

Montes D., De Castro E., Cornide M.

1994, I Reunión Científica de la Sociedad Española de Astronomía.

ABSTRACT


Se presentan observaciones espectroscópicas de resolución intermedia en la región de la línea Hβ de cinco sistemas binarios con actividad cromosférica (AR Psc, UX Ari, V833 Tau, KZ And, II Peg).
Se ha aplicado la técnica de subtracción de un espectro sintético obtenido con estrellas no activas del mismo tipo espectral y clase de luminosidad que el sistema estudiado, para poner de manifiesto el posible llenado de la absorción Hβ por emisión cromosférica. De esta forma se ha determinado cual es la componente del sistema binario responsable de la emisión y se han medido la anchura equivalente (EW) del exceso de emisión en Hβ. En los cinco sistemas se ha encontrado un exceso de emisión Hβ importante cuya intensidad esta fuertemente relacionada con el comportamiento observado en la línea Hα.
En aquellos sistemas en los que también se disponía de observaciones en Hα(Montes et al. 1994) se ha estudiado el cociente entre los excesos de emisión en ambas líneas (EW(Hα)/EW(Hβ), el cual proporciona información (Buzasi 1993) sobre las regiones en las que se originan estas emisiones, permitiendo determinar si la emisión procede de regiones activas vistas sobre el disco, o si proviene de material extenso visto sobre el limbo (protuberancias).


Flux-flux relations between excess Hα, Ca II H & K and Hε emissions and other activity indicators in chromospherically active binaries

Montes D., Fernández-Figueroa M.J., Cornide M., De Castro E.,

1996, Cool Stars, Stellar Systems, and the Sun 9th Cambridge Workshop, R. Pallavicini & A.K. Dupree (eds.), ASP Conference Series 109, 657

ABSTRACT


A sample of 83 chromospherically active binary systems including the RS Canum Venaticorum binaries (RS CVn) and BY Draconis (BY Dra) classes has been studied by using the spectral subtraction technique (subtraction of a synthesized stellar spectrum constructed from reference stars of spectral type and luminosity class similar to those of the binary star components). With this technique we have obtain the active-chromosphere contribution to the Hα line in 51 systems, and to the Ca II H & K lines in 73 systems and 19 single active stars.
The derived excess Hα emission fluxes have been compared with those obtained in the Ca II K and Hε lines finding a good correlation between these three chromospheric activity indicators. The Hα losses seem to be more important than Ca II K losses for cooler stars, in fact, all the system with Hα emission above the continuum are cooler than 5000 K. The Hε emission line appears to be an alternative activity indicator.
Correlations between the excess Hα and Ca II K emissions and other activity indicators, (C IV in the transition region, and X-rays in the corona) indicate that the exponents of the power-law relations increase with the formation temperature of the spectral features.


Excess Hβ emission in five chromospherically active binaries

Montes D., Fernández-Figueroa M.J., De Castro E., Cornide M.

1995, Stellar Surface Structure, IAU Symp 176, Poster Proceedings, Strassmeier K. (ed), p. 167

ABSTRACT


Enhanced emission cores in the Ca II resonance lines H and K, are the primary optical indicators of chromospheric activity. However, the Balmer Hα and Hβ lines can also be used as chromospheric activity indicators, especially in the chromospherically active binary systems (RS CVn and BY Dra) characterized by high levels of activity.
First observations of Balmer Hα line in late type stars showed that the line can appear with a core in absorption or in emission. Lately, a filling-in of the central core of the Hα line by chromospheric activity has been reported in single stars and in chromospherically active binaries (Strassmeier et al. 1990; Fern\'andez-Figueroa et al. 1994, hereafter FFMCC; Eker et al. 1994; Frasca & Catalano 1994; and Montes et al. 1995a, b).
For chromospherically active binary systems a different behaviour of the Hα and Hβ line profiles with the photometric wave has been noted and so, several assumptions about the emitting regions have been proposed: emission arising from regions concentrated around starspots, from network-like structures, or from prominence-like material (Hall & Ramsey 1992).
We report high resolution observations of the Balmer Hβ line in five chromospherically active binaris (AR Psc, UX Ari, V833 Tau, KZ And, II Peg). The component in the binary responsible for the Hβ emission has been identified and the excess Hβ emission equivalent width (EW) for these stars has been determined.
When observations of these systems in the region of the Hα line are also available (Montes et al. 1995a, b) we have used the ratio of excess emission in Hα and Hβ as a diagnostic for discriminating between the presence of plages and prominences in the stellar surface, following the results of Hall & Ramsey (1992) and Buzasi (1993) who found that low EHα/Eβ} ($\approx$~1-2) can be achieved both in plages and prominences viewed against the disk, but that high ratios ($\approx$~3-15) can only be achieved in extended regions viewed off the limb.


Citations



The broad components in the Hα line of very active stars: chromospheric microflaring?

Montes D., Fernández-Figueroa M.J., De Castro E., Cornide M., Poncet A., Sanz-Forcada J.,

1998, in ASP Conf. Ser. 154, Cool Stars, Stellar Systems, and the Sun, 10th Cambridge Workshop , eds. R.A. Donahue & J.A. Bookbinder (San Francisco: ASP), CD-1516

ABSTRACT


In our analysis of the Hα line, using the spectral subtraction technique, in chromospherically active binary systems and in weak-lined T Tauri stars (WTTS), we have found that in some stars the subtracted Hα emission line profile has very broad wings, and is not well matched using a single-Gaussian fit. These profiles have therefore been fitted using two Gaussian components: a narrow component having a FWHM of 45-90 km/s and a broad component with a FWHM ranging from 133 to 470 km/s. This broad component could be interpreted as arising from microflaring that occurs in the chromosphere by similarity with the broad components also found by other authors in the chromospheric MgII h & k lines and in several transition region lines of active stars. The microflares are frequent, short-duration, energetically weak disturbances, i.e. they are the low-energy extension of flares, and therefore have large-scale motions associated that could explain the broad wings observed in these lines. A correlation between the contribution of the broad components and the degree of stellar activity seems to be present. In some cases the line is asymmetric and the fit is better matched when the broad component is blue-shifted or red-shifted with respect to the narrow component. These asymmetries are also observed during the impulsive and gradual phases of solar and stellar flares, and favour the interpretation of the broad component as due to upward and downward motions produced by microflaring in the chromosphere.


Citations



The chromospheric activity of weak-lined T Tauri stars: simultaneous Hα and Ca II H & K observations
Poncet A., Montes D., Fernández-Figueroa M.J., Miranda L.F.,

1998, in ASP Conf. Ser. 154, The Tenth Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun , eds. R.A. Donahue & J.A. Bookbinder (San Francisco: ASP), CD-1772

ABSTRACT


Simultaneous Halpha and Ca ii H & K spectroscopic observations are reported here for 20 weak line T Tauri stars (WTTS) with photometric rotational periods well determined. In the WTTS, contrary to the classical T Tauri stars (CTTS), the emission lines are not influenced by the presence of circumstellar disks and accretion processes and the chromospheric contribution to these lines may be determined by means of the spectral subtraction technique. By using these chromospheric excess emissions we will study the flux-flux and rotation-activity relationships in order to get insights into the mechanisms which drive solar-like stellar activity in this kind of low mass pre-main sequence stars. We discuss here in more detail preliminary results for three WTTS: V773 Tau and V410 Tau which present short term chromospheric variability , and LkCa7 which shows strong emission in the Halpha, higher Balmer lines (Hdelta, Hepsilon, Hzeta, Heta and Htheta) and Ca ii H & K lines. Very broad wings have been found in the subtracted Halpha profile of V773 Tau and V410 Tau, which could be interpreted as arising from microflaring.


Citations



Late-type stars members of young stellar kinematic groups

Montes D., Latorre A., Fernández-Figueroa M.J.

2000, in ASP Conf. Ser. 198, 203: Stellar clusters and associations: convection, rotation, and dynamos
(Second "Three-Islands" Euroconference) (May 25 - 28, 1999, Mondello, Palermo, Sicily, Italy)
R. Pallavicini, G. Micela and S. Sciortino eds.
PS_file -- astro-ph/9906069 -- ADS Abstract
Available via WWW


Citations



Chromospherically active binaries members of young open clusters

Montes D.,

2000, in ASP Conf. Ser. 198, 475: Stellar clusters and associations: convection, rotation, and dynamos
(Second "Three-Islands" Euroconference) (May 25 - 28, 1999, Mondello, Palermo, Sicily, Italy)
R. Pallavicini, G. Micela and S. Sciortino eds.
PS_file -- ADS Abstract
Available via WWW


Citations



Publicaciones DMG

David Montes, dmgastrax.fis.ucm.es