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Start Over Subject late-type stars Facility ROSAT
1. F, G and K stars BVRI photometry
ID:
ivo://CDS.VizieR/J/A+AS/131/197
Title:
F, G and K stars BVRI photometry
Short Name:
J/A+AS/131/197
Date:
15 Dec 2021 08:12:40
Publisher:
CDS
Description:
We present accurate BV(RI)c photometry for a sample of F, G and K stars detected in selected areas of the ROSAT all-sky survey (RASS). We have used the photometry, in addition to low-resolution spectroscopy, to estimate spectral classifications, distances and X-ray luminosities. The log(L_X_/L_V_) in the sample lies below -2. Although the sample contains also nearby, inactive stars, it is dominated by active objects. The median X-ray luminosity in our sample is <L_X_>=29.88 and the mean value of the hardness ratios <HR1>=0.13+/-0.35. We compare the derived X-ray luminosity function with similar functions obtained from the serendipitous samples of the Einstein Observatory medium sensitivity survey (EMSS, Cat. <IX/15>) and EXOSAT (Cat. <J/A+AS/115/41>). Our sample is completely consistent with the EMSS sample of solar type stars, indicating that both our sources and the EMSS sources are representative of the high galactic latitude X-ray stellar population. We do not find extremely active stars (log(L_X_)>=32), as are found in the EMSS sample, and we argue that these objects are rare.
2. High-resolution spectra south of Taurus
ID:
ivo://CDS.VizieR/J/A+A/325/647
Title:
High-resolution spectra south of Taurus
Short Name:
J/A+A/325/647
Date:
21 Oct 2021
Publisher:
CDS
Description:
Listed are results from our high-resolution data for all stars in our study area which were listed by either Magazzu et al. (1997A&AS..124..449M) or Alcala et al. (1996A&AS..119....7A), i.e. T Tauri candidates from the ROSAT All-Sky Survey. In table 1, we list all stars for which lithium was found either by Magazzu et al. (1997A&AS..124..449M) or in our CASPEC spectra, as well as two stars identified as wTTS by Alcala et al. (1996A&AS..119....7A). Listed are the designation, number of single-order echelle spectra taken, effective temperatures, projected rotational velocities, mean heliocentric radial velocities with errors, radial velocities in the local standard of rest, and remarks on variability in radial velocity as found in our high-resolution spectra. For comparison, we also list the results on spectral types of the stars (with `e' for H{alpha} emission) as found by Magazzu et al. (1997A&AS..124..449M) (or Alcala et al., 1996A&AS..119....7A) with low- and medium-resolution spectroscopy. In the last two columns, we list the (NLTE) lithium abundance (given on a scale where logN(H)=12) and the lithium excess above the relevant Pleiades upper envelope; upper limits indicate stars where the Magazzu et al. (1997A&AS..124..449M) spectra suffer from either low S/N or low resolution. In table 2, we list all stars where no lithium was detected -- neither by Magazzu et al. (1997A&AS..124..449M) nor in our CASPEC spectra.
3. Proper motions of faint ROSAT WTT stars
ID:
ivo://CDS.VizieR/J/A+A/341/L79
Title:
Proper motions of faint ROSAT WTT stars
Short Name:
J/A+A/341/L79
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present proper motions of 59 stars of the ROSAT All-Sky Survey (RASS) located in direction of the Chamaeleon star forming region (SFR) in the magnitude range B=5.1-17mag. Proper motions of the fainter stars were newly derived utilizing survey Schmidt plates from the GSC~II plate archive and from a set of special plates taken with the ESO Schmidt telescope. The vector point diagram (VPD) indicates that the certified weak emission-line T Tauri (WTT) stars cluster away from the region occupied by the brighter pre-main-sequence stars (PMS) in Cha I. The distance to this new association is estimated at ~100pc, sensibly smaller than the 150pc generally assumed for the SFR. This yields an upper limit of 2km/s for the velocity dispersion of this new kinematic group. The de-reddened CM diagram of the group members suggest the WTT stars are still PMS objects, but older (3-30Myr) and less massive than previous determinations. These revised age estimates, the newly derived group peculiar velocity, and current distance estimates to the Cha~I/II/III complex would favour in-situ formation against that predicted by high velocity cloud models. Finally, based on a redetermination of the peculiar motions of stars and gas, we speculate that the whole SFR originated from the local Orion spur as a result of more classical mechanisms like interactions with the spiral arms.
4. ROSAT data of Nearby Stars
ID:
ivo://CDS.VizieR/J/A+AS/135/319
Title:
ROSAT data of Nearby Stars
Short Name:
J/A+AS/135/319
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present X-ray data for all entries of the Third Catalogue of Nearby Stars (Gliese and Jahreiss, 1991, Cat. <V/70>) that have been detected as X-ray sources in the ROSAT all-sky survey. The catalogue contains 1252 entries yielding an average detection rate of 32.9 percent. In addition to count rates, source detection parameters, hardness ratios, and X-ray fluxes we also list X-ray luminosities derived from Hipparcos parallaxes.

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