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Low-mass spectroscopic binaries in the Hyades: a candidate brown dwarf companion
We have used the HIRES echelle spectrograph on the Keck I telescope toobtain high-resolution spectroscopy of 51 late-type M dwarfs in theHyades cluster. Cross-correlating the calibrated data against spectra ofwhite dwarfs allows us to determine heliocentric velocities with anaccuracy of +/-0.3kms-1. 27 stars were observed at two epochsin 1997; two stars, RHy 42 and RHy 403, are confirmed spectroscopicbinaries. RHy 42 is a double-lined, equal-mass system; RHy 403 is asingle-lined, short-period binary, P~1.275d. RHy 403A has an absolutemagnitude of MI=10.85, consistent with a mass of0.15Msolar. The systemic mass function has a valueM2sin(i)]3/(M1+M2)2=0.0085, which, combined with the non-detection of a secondary peak inthe cross-correlation function, implies0.095>M2>0.07Msolar, and the strongpossibility that the companion is the first Hyades brown dwarf to beidentified. Unfortunately, the maximum expected angular separation inthe system is only ~0.25mas. Five other low-mass Hyads are identified aspossible spectroscopic binaries, based either on repeat observations oron a comparison between the observed radial velocity and the valueexpected for Hyades cluster members. Combined with HST imaging data, weinfer a binary fraction between 23 and 30per cent. All of the stars arechromospherically active. RHy 281 was caught in mid-flare and, based onthat detection, we estimate a flaring frequency of ~2.5per cent forlow-mass Hyades stars. Nine stars have rotational velocities, vsin(i),exceeding 20kms-1, and most of the sample have detectablerotation. We examine the H&alpha emission characteristics oflow-mass cluster members, and show that there is no evidence for acorrelation with rotation.
| Low-Mass Binaries in the Hyades: A Scarcity of Brown Dwarfs
Abstract image available at:http://adsabs.harvard.edu/abs/1997AJ....114.1992R
| UBVRI Standard Stars at Northern Declinations
Accurate values of V, B--V and U--B are given 123 stars of magnitudesfrom 6 to 11 at high northern declinations. For 36 stars also V--R andR--I color indices are given.
| A study of some stars with circumstellar dust envelopes. I
We present the results of a study of circumstellar dust envelopes of 36stars of early(O-B-A) types in the directions of the associations CasOB1, Cas OB2, Per OB1, and Ori OB1. We determine the absorption at 1640Å, the linear radius of the dust envelopes, the mean value of thecoefficient k, and the masses of the envelopes. They differsignificantly from one another.
| The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars
The Henry Draper Extension Charts (HDEC), published in the form offinding charts, provide spectral classification for some 87000 starsmostly between 10th and 11th magnitude. This data, being highlyvaluable, as yet was practically unusable for modern computer-basedastronomy. An earlier pilot project (Roeser et al. 1991) demonstrated apossibility to convert this into a star catalogue, using measurements ofcartesian coordinates of stars on the charts and positions of theAstrographic Catalogue (AC) for subsequent identification. We presenthere a final HDEC catalogue comprising accurate positions, propermotions, magnitudes and spectral classes for 86933 stars of the HenryDraper Extension Charts.
| Chromospheric and coronal activity in low-mass Hyades dwarfs
We present an extensive survey of the chromospheric and coronal activityamong low-mass members of the Hyades open cluster. We have obtained Halpha spectroscopy of 91 probable cluster members, including 23 that liewithin three fields for which we have deep ROSAT X-ray observations. 20of the 23 stars are detected in X-rays; the non-detections are probablynot Hyades members. Combining these observations with data from theliterature, we find that the mean H alpha to bolometric luminosity ratiolog (L_H alpha/L_bol) is constant at a value of ~-3.9 for M_bol>8,with a substantial dispersion and an upper limit of -3.5. The X-ray tobolometric luminosity ratio log (L_x/L_bol) first increases withincreasing M_bol, then flattens at a value of ~-3.3 for M_bol>8.Comparing this behaviour with stars in the Pleiades cluster, there aresignificant differences: first, the log (L_H alpha/L_bol) ratioincreases with increasing M_bol while M_bol<10, but appears to turnover sharply at fainter magnitudes, with the lower luminosity starsbeing nearly an order of magnitude lower in the ratio; secondly, we findno evidence for saturation in the log (L_x/L_bol) ratio; L_x increasesmonotonically with M_bol, reaching a value of ~-2.5 at M_bol~10. Lowerluminosity stars have not yet been detected in X-ray observations. Thenearly constant H alpha to H beta ratio in the Hyades stars, coupledwith the small range in coronal temperature seen in the X-ray data,suggest that the (presumably magnetically generated) heating rate isnearly constant in the outer atmospheres of these stars. Differences inthe relative activity levels are then ascribed to differences in thefilling factor of active regions, and in the sizes of the coronalstructures.
| Low-Mass Stars in the Hyades
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993MNRAS.265..785R&db_key=AST
| The low mass Hyades and the evaporation of clusters
The 135 single stars and 85 binary systems, redder than R-I = +0.34 magand brighter than V = 17 mag, between alpha = 3.75 h and 5.0 h and delta= +5 deg and + 25 deg show a luminosity function that differsconsiderably from that of the general field stars within 20 pc of theSun. The ratio of double star components to single cluster membersincreases markedly with decreasing luminosity. Forty-three single starsand 16 binary systems that are members of the Hyades supercluster within20 pc of the Sun show the same luminosity function as the field stars inthat region. Fifty percent of the cluster members and 40 percent of thesupercluster members are components of binary stars. The equivalentwidths of H-alpha appear to support a range of ages (approximately 8 to16 x 108 yr) for the cluster stars and demonstrate that theoldest objects are in the supercluster. A list of cluster members, whichmay include the end of the stable main sequence, but for which accurate(R-I) photometry is not available, is included. The half-dozen knownparallax stars of the faintest luminosity contain at least onesupercluster member, TVLM 868-110639, which is probably beyond thestable, nuclear burning main sequence as a 'transitional' or 'brown'dwarf.
| Proper motions from Schmidt plates. II - The Hyades
COSMOS scans of photographic plates taken by the Palomar Oschin Schmidttelescope and by the UK Schmidt telescope are used to obtain propermotions for about 450,000 stars within a 112-sq-deg region covering partof the Hyades luster. With epoch differences of 33 to 37 yr, propermotions accurate to 6-12 milliarcsec/yr are obtained, and 393 candidateHyades to a limiting magnitude of about 15.5, including at least two newwhite dwarf candidates, are identified. The main-sequence luminosityfunction determined from this sample is similar to that defined by localfield stars, with a broad maximum at about +12. Both the line-of-sightand surface density distributions show evidence for significant masssegregation; the overall proper motion distribution suggests a tightcore centered within a much broader distribution. A total mass of410-480 solar masses and a gravitational binding radius of about 10.5 pcare derived.
| A radial-velocity survey of the Hyades
Photoelectric radial-velocity measurements, obtained with external erroras small as 0.1 km/s using the 200-inch Hale telescope at PalomarObservatory during the period 1971-1986, are reported for over 400candidate members (with V magnitude between 6 and 14) of the Hyadescluster. The history of Hyades observations is recalled; the Palomarinstrumentation and observing program are described; the data-reductionand standardization procedures are discussed in detail; and the data arepresented in extensive tables and graphs. About 200 of the stars areclassified as cluster members, including 60 spectroscopic binaries.
| Photometry of possible members of the Hyades cluster. VII
Photoelectric observations in BVRI colors have been obtained for 156stars, 124 of them without previous photometry, which have beensuspected of being members of the Hyades star cluster on the basis oftheir proper motion. About half appear to be probable or possiblecluster members, and of these, about one-quarter lie outside the tidalradius of the cluster. Most of the stars included here are faint andwere without published finding charts. Their identifications wereconfirmed form motions observed on plates taken in the course of theLick Northern Proper Motion Survey, and we provide finding charts forthem. This list raises to over 700 the number of Hyades candidates thathave been observed during the course of this photometric survey. Roughlyhalf of these appear to be probable or possible cluster members.
| A study of the motion, membership, and distance of the Hyades cluster
Particular attention is given to the role of the convergent-point, ormoving cluster, method in the determination of the Hyades distance, andthe apparent discrepancy between its results and those of other Hyadesdistance indicators. The Hyades photographic plate material isconsidered along with the approaches used in the measurements, propermotion reductions, coordinate reductions, and aspects of photography.Problems of cluster membership determination are also discussed.
| Low-luminosity members of the Hyades cluster. II.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969AJ.....74....2V&db_key=AST
| Low-luminosity members of the Hyades cluster.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1966AJ.....71..482V&db_key=AST
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Наблюдательные данные и астрометрия
| Созвездие: | Телец |
| Прямое восхождение: | 04h18m17.65s |
| Склонение: | +15°00'33.8" |
| Видимая звёздная величина: | 9.46 |
| Собственное движение RA: | 89 |
| Собственное движение Dec: | -96.4 |
| B-T magnitude: | 10.61 |
| V-T magnitude: | 9.555 |
Каталоги и обозначения:
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