M. C. Gálvez

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

This is the first paper of a series aimed at studying the properties of late-type members of young stellar kinematic groups. We concentrate our study on classical young moving groups such as the 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 on recently identified groups such as the Castor moving group (200 Myr). In this paper we compile a preliminary list of single late-type possible members of some of these young stellar kinematic groups. Stars are selected from previously established members of stellar kinematic groups based on photometric and kinematic properties as well as from candidates based on other criteria such as their level of chromospheric activity, rotation rate and lithium abundance. Precise measurements of proper motions and parallaxes taken from the Hipparcos Catalogue, as well as from the Tycho-2 Catalogue, and published radial velocity measurements are used to calculate the Galactic space motions (U, V W) and to apply Eggens 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 substellar companions.

Multiwavelength optical observations of two chromospherically active binary systems: v789 mon and gz leo

This paper describes a multiwavelength optical study of chromospheres in two X-ray/EUV-selected active binary stars with strong H alpha 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 (v sin i) and the equivalent width of the lithium Li i λ6707.8 A absorption line were determined.

Multiwavelength optical observations of chromospherically active binary systems - IV. The X-ray/EUV selected binary BK Psc (2RE J0039+103)

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 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 (M sin^3 i) 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 (v sin i, 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 line 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. Hα 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 Hα and Hβ emission seems to arise from prominence-like material, and the Ca II IRT emission from plage-like regions.

Spectroscopic Analysis of the Extremely Active Binaries: BK Psc and XX Tri

We present here high resolution echelle spectroscopic observations of two extremely active binaries (BK Psc and XX Tri). Spectra have been taken in July 1999 using the FOCES spectrograph with the 2.2 m telescope in Calar Alto (Almeria) and in November 1999 using the SOFIN spectrograph at the Nordic Optical Telescope (NOT) (La Palma). These multiwavelength optical observations allow us to study the chromosphere of these active binary systems using the information provided for several optical spectroscopic features (from the Ca II H & K to Ca II infrared triplet (IRT) lines) formed at different heights in the chromosphere. The chromospheric contribution in these lines has been determined using the spectral subtraction technique. We have determined radial velocities, rotational velocities (V sin i) and lithium (Li I λ6707.8) equivalent widths.

FR Cnc Nature Revisited

The results of photometric and spectroscopic monitoring of FR Cnc reported a tricky nature. We carried out several observations at different observatories in India, Russia, Ukraine and Spain during several years to characterize and discover the source of its radial velocity (RV) variations. After discarding a binary nature in first instance due to its high level of activity, further detailed and complete study lead as to still take into account the presence of a stellar companion possibility. We present here the study of this star and preliminary conclusions about its real nature.

And the Oscar Goes to: BD+20 1790 for “The Mystery of the Unseen Companion“

BD+20 1790 is a young, rich metal and very active late–type K5Ve star. Our group has been developing a study of stellar activity and kinematics for this star over the past years. Previous results show a high level of stellar activity, with the presence of prominence-like structures, spots on surface and strong flare events. Radial velocity (RV) variations with a semi-amplitude of up to 1km s−1 were detected. When the nature of these variations was investigated it was found that they are not due to stellar activity. Based upon the analysis of bisector velocity span, as well as Ca ii H & K emission, we report that the best explanation for RV variations is the presence of a sub–stellar companion. The Keplerian fit of the RV data yields an orbital solution for a close-in massive planet with an orbital period of 7.783days. Also, the presence of this close–in massive planet could be an interpretation for the high level of stellar activity detected.

BD+20 1790 b: Chronicle of an exoplanetary discovery

In this contribution we report evidence for a planetary companion around a young and active late‐type K star. Our group has been developing a study of stellar activity and kinematics for this star over the past years. Previous results show a high level of stellar activity, with the presence of prominence‐like structures, spots on surface and strong flare events. Radial velocity (RV) variations with a semi‐amplitude of up to 1 km s^(−1) were detected. When the nature of these variations were investigated it was found that they are not due to stellar activity. Based upon the analysis of bisector velocity span, as well as Ca II H & K emission, we report that the best explanation for RV variation is the presence of a sub‐stellar companion. The Keplerian fit of the RV data yields an orbital solution for a close‐in massive planet with an orbital period of 7.783 days. Also, the presence of this close‐in massive planet chould be an interpretation for the high level of stellar activity detected.

EUVE J0825-16.3 and EUVE J1501-43.6: Two dMe Double–Lined Spectroscopic Binaries

High-resolution echelle spectroscopic observations taken with the FEROS spectrograph at the ESO 2.2-m telescope confirm the binary nature of the dMe stars EUVE J0825−16.3 and EUVE J1501−43.6, previously reported by Christian & Mathioudakis (2002). In these binary systems, emission of similar intensity from both components is detected in the Na i D 1 & D 2 , He i D 3 , Ca II H&K, Ca II IRT and Balmer lines. We have determined precise radial velocities by cross-correlation with radial velocity standard stars, which have allowed us to obtain for the first time the orbital solution of these systems. Both binaries consist of two nearly equal M0V components with an orbital period shorter than 3.5 days. We have analyzed the behaviour of the chromospheric activity indicators (variability and possible flares). In addition, we have determined its rotational velocity and kinematics.

Multiwavelength Optical Observations of Three X Ray/EUV Selected Binaries

In this contribution we present high resolution echelle spectroscopic observations of three recently discovered, X-ray/EUV selected, active binaries (2RE J0933+624, 2RE J1101+223, 2RE J0725-002).

The Local Association Moving Group: Late-Type Members and Age Subgroups

The Local Association or Pleiades moving group (MG) seems to consist of a reasonably coherent kinematic stream of young stars with embedded clusters and associations. The age of the stars in this association range from about 20 to 150 Myr. Evidences have been found that X-ray and EUV selected active stars and lithium-rich stars are member of this association. Recently, several studies using extended samples of stars (mainly early-type stars) with known radial velocities and astrometric data taken from Hipparcos not only confirm the existence of this moving group, but also detect finer structures.