|A Census of the Young Cluster IC 348|
We present a new census of the stellar and substellar members of theyoung cluster IC 348. We have obtained images at I and Z for a42'×28' field encompassing the cluster andhave combined these measurements with previous optical and near-infraredphotometry. From spectroscopy of candidate cluster members appearing inthese data, we have identified 122 new members, 15 of which havespectral types of M6.5-M9, corresponding to masses of ~0.08-0.015Msolar by recent evolutionary models. The latest census forIC 348 now contains a total of 288 members, 23 of which are later thanM6 and thus are likely to be brown dwarfs. From an extinction-limitedsample of members (AV<=4) for a16'×14' field centered on the cluster, weconstruct an initial mass function (IMF) that is unbiased in mass andnearly complete for M/Msolar>=0.03 (<~M8). Inlogarithmic units where the Salpeter slope is 1.35, the mass functionfor IC 348 rises from high masses down to a solar mass, rises moreslowly down to a maximum at 0.1-0.2 Msolar, and then declinesinto the substellar regime. In comparison, the similarly derived IMF forTaurus from Briceño et al. and Luhman et al. rises quickly to apeak near 0.8 Msolar and steadily declines to lower masses.The distinctive shapes of the IMFs in IC 348 and Taurus are reflected inthe distributions of spectral types, which peak at M5 and K7,respectively. These data provide compelling, model-independent evidencefor a significant variation of the IMF with star-forming conditions.Based on observations obtained at Keck Observatory, Steward Observatory,the MMT Observatory, and the Canada-France-Hawaii Telescope. Thispublication makes use of data products from the Two Micron All SkySurvey, which is a joint project of the University of Massachusetts andthe Infrared Processing and Analysis Center/California Institute ofTechnology, funded by the National Aeronautics and Space Administrationand the National Science Foundation.
|Search for solid HDO in low-mass protostars|
We present ground-based 2.1 to 4.2 mu m observations of four low-massprotostars. We searched for the 4.1 mu m OD stretch band, characteristicof solid HDO in grain mantles. We did not detect solid HDO in any of thefour sources, but we derive 3sigma upper limits from 0.5% to 2% for theHDO/H_2O ratio depending on the source. These ratios provide strongconstraints to solid-state deuteration models when compared to deuteriumfractionation values observed in the gas phase. We discuss variousscenarios that could lead to such a low water deuteration compared tothe high formaldehyde and methanol deuteration observed in thegas-phase.
|Low-Mass Star Formation and the Initial Mass Function in IC 348|
We have performed deep infrared and optical spectroscopy of virtuallythe entire stellar population within the 5' x 5' core of IC 348,measuring K (2.2 μm) band and optical spectral types that are in goodagreement. We have also identified several sources that may besubstellar depending on the choice of temperature scales andevolutionary tracks, with three particularly late-type objects (M7.5-M8)that are likely bonafide brown dwarfs. In conjunction with thetheoretical evolutionary tracks of D'Antona & Mazzitelli, the H-Rdiagram indicates a spread in ages from 0.5 to 10 Myr, with most of thecore star formation occurring in the last 3 Myr. Using K-band imaging toprovide a completeness correction to the spectroscopic sample, we arriveat an initial mass function (IMF) that matches that of Miller &Scalo from 0.25 to 3 M_ȯ. The IMF appears to fall slowly from 0.25M_ȯ to the hydrogen burning limit, slightly below the IMF of Miller& Scalo, which is flat in logarithmic units (as compared to slopesof ~1.35 and -2.6 for Salpeter and Scalo). Correction for unresolvedbinary systems could steepen the slope of the low-mass IMF by about 0.5,which implies a single-star IMF that is roughly flat below 0.25M_ȯ. The low-mass IMF in IC 348 is similar to that derived instudies of most other young clusters, implying that the IMF does notvary dramatically among clusters of differing environments; however, thederived IMF is dependent on the evolutionary tracks and the detailedshape of the IMF should be viewed with caution until these models aretested against observations, particularly at low masses (<0.3M_ȯ) and young ages (<10 Myr). Hα and Brgamma emissionstrengths are consistent with predictions of magnetospheric accretionmodels of Muzerolle, Calvet, & Hartmann for accretion rates of10^-9-10^-8 M_ȯ yr^-1. Combining our data with the Hαmeasurements of Herbig, we find that ~25% of stars within the core of IC348 and younger than 3 Myr exhibit signatures of disks in the form ofstrong Hα (>10 Å) or Brgamma (>1 Å) emission orK-band continuum veiling (r_K >= 0.5). Since no sources older than 3Myr show evidence for massive disks, disk lifetimes in the core of IC348 appear to be shorter than those observed in Taurus or in the outerregions of IC 348.
|The ROSAT all-sky survey catalogue of optically bright main-sequence stars and subgiant stars|
We present X-ray data for all main-sequence and subgiant stars ofspectral types A, F, G, and K and luminosity classes IV and V listed inthe Bright Star Catalogue that have been detected as X-ray sources inthe ROSAT all-sky survey; several stars without luminosity class arealso included. The catalogue contains 980 entries yielding an averagedetection rate of 32 percent. In addition to count rates, sourcedetection parameters, hardness ratios, and X-ray fluxes we also listX-ray luminosities derived from Hipparcos parallaxes. The catalogue isalso available in electronic form via anonymous ftp tocdsarc.u-strasbg.fr (126.96.36.199) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
|Photovisual Magnitude Differences for 169 Double Stars|
Photovisual magnitude differences determined from multi-exposurephotographic plates for 169 double stars are presented. The separationsrange from 1.5'' to 113\arcsec, and the photovisual magnitudedifferences vary from 0.03 to 6.14 magnitudes. The internal mean errorof a single magnitude difference estimate is +/-0.064 magnitude.
|Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.|
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
|Observation of fine structure in the cold phase of the local interstellar medium using K I absorption|
The K I 7699-A resonance absorption line was used to observe a group of18 early-type stars within a 200-pc radius of the sun with asignal-to-noise ratio of 50-250. The interstellar absorptions provide away to 'tag' a cloud via its radial velocity to within +/-1.5 km/s.Based on the hypothesis of pressure confinement, the temperatures of theclouds are estimated at 100 K or less. The mass fraction of the localinterstellar medium (LISM) is found to be high in these clouds, at least80 percent of the total, whereas the filling factor is low, well below10 percent of the total LISM volume. One cloud with high densities andlower temperatures was detected which is thought to be on the edge ofatomic-molecular equilibrium.
|UBV photometry of stars whose positions are accurately known. VI|
Results are presented from UBV photometric observations of 1000 stars ofthe Bright Star Catalogue and the faint extension of the FK5.Observations were carried out between July 1987 and December 1990 withthe 40-cm Cassegrain telescope of the Kvistaberg Observatory.
|Third preliminary catalogue of stars observed with the photoelectric astrolabe of the Beijing Astronomical Observatory.|
|Photoelectric photometry of the AM star HR 976 = V 423 Per|
This spectroscopic binary is the largest amplitude variable among Amstars. UBV observations of the star are presented. They show that in1964 and 1965 it was constant in B and was only marginally variable inU. The hypothesis of the ellipsoidal variability of HR 976 is thendiscussed and found untenable. It is pointed out that this result mayreopen the issue of light variability of Am stars.
|Photoelectric observations and extinction of the irregular variable IP Per.|
|Late B-type stars - Rotation and the incidence of HgMn stars|
High-dispersion spectrograms for an unbiased sample of 256 late B-typestars are examined in an attempt to determine whether slow rotation isnecessary and sufficient for the appearance of HgMn anomalies innonmagnetic stars. The peculiar stars in the sample are identified,values of v sin i are derived for all the stars observed, and theradial-velocity variations of the identified HgMn stars are analyzed.The distribution of rotational velocities for late B-type stars isobtained, and the role of rotation in producing extended envelopes isevaluated. The binary frequency and mass-ratio distribution are derivedfor systems containing HgMn components, the effect of duplicity on thedistribution of rotational velocities is estimated, and the role of suchfactors as rotation, age, and binary characteristics in determiningwhether HgMn anomalies are present is investigated. The results clearlyshow that HgMn stars occur only within a limited temperature range, thatall such stars rotate slowly, but that rotation, effective temperature,age, surface gravity, and binary properties do not serve to determinewhether a star will exhibit abundance anomalies.
|Spectral classification from the ultraviolet line features of S2/68 spectra. III - Early A-type stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978A&AS...33...15C&db_key=AST
|Positions moyennes et mouvements propres de 355 etoiles DU GC de la zone de declinaison +33 +36.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976A&AS...26..219M&db_key=AST
|Rotational Velocities of a0 Stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974ApJS...28..101D&db_key=AST
|Four-color and Hβ photometry for the brighter AO type stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&AS....5..109C&db_key=AST
|A catalogue of proper motions for 437 A stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970A&AS....1..189F&db_key=AST
|Photoelectric observations of early A stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970A&AS....1..165J&db_key=AST
|Stars with large proper motions in the Astrographic zones + 32° and + 33° (List III)|