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A Census of the Chamaeleon I Star-forming Region
I present a new census of the members of the Chamaeleon I star-formingregion. Optical spectroscopy has been obtained for 179 objects that havebeen previously identified as possible members of the cluster, that lackeither accurate spectral types or clear evidence of membership, and thatare optically visible (I<~18). I have used these spectroscopic dataand all other available constraints to evaluate the spectralclassifications and membership status of a total sample of 288 candidatemembers of Chamaeleon I that have appeared in published studies of thecluster. The latest census of Chamaeleon I now contains 158 members,eight of which are later than M6 and thus are likely to be brown dwarfs.I find that many of the objects identified as members of Chamaeleon I inrecent surveys are actually field stars. Meanwhile, seven of ninecandidates discovered by Carpenter and coworkers are confirmed asmembers, one of which is the coolest known member of Chamaeleon I at aspectral type of M8 (~0.03 Msolar). I have estimatedextinctions, luminosities, and effective temperatures for the membersand used these data to construct an H-R diagram for the cluster.Chamaeleon I has a median age of ~2 Myr according to evolutionary modelsand hence is similar in age to IC 348 and is slightly older than Taurus(~1 Myr). The measurement of an initial mass function for Chamaeleon Ifrom this census is not possible because of the disparate methods withwhich the known members were originally selected and must await anunbiased, magnitude-limited survey of the cluster.Based on observations performed at Las Campanas Observatory. 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.
| Classification and properties of UV extinction curves
The catalog of Savage et al. (\cite{ref27}) reporting colour excesses of1415 stars from ANS photometry offers the opportunity to deeplyinvestigate the characteristics of UV extinction curves which differfrom the standard extinction of the diffuse interstellar medium. To thisaim we have selected a sample of 252 curves, which have been comparedwith the relations derived by Cardelli et al. (\cite{ref4}; CCM in thefollowing) for a variety of R_V values in the range 2.4-5 and have beenclassified as normal if they fit at least one of the CCM curves oranomalous otherwise. We find that normal curves with small R_V are justas numerous as those with large R_V. The anomalous objects are arrangedinto two groups according to the strength of the bump at 0.217 mu . Fora given value of c_2 this increases along the sequence: type Aanomalous, normals and type B anomalous, suggesting that this sequenceshould correspond to an increase of the amount of small grains along thesightline. Considerations concerning the environmental characteristicsindicate that the anomalous behaviour is not necessarily tied to theexistence of dense gas clouds along the line of sight.
| On the distance to the Chamaeleon I and II associations
Constraints on the distances to the dark clouds Chamaeleon I and II areinvestigated in detail. A compilation of photometric data, spectraltypes and absolute magnitudes for field stars towards each cloud ispresented, and results are used to examine the distribution of reddeningwith distance along each line of sight. The distances to starsassociated with reflection nebulae in each cloud are examined in detail.On the basis of these results, we deduce the most probable distance ofCha I to be 160+/-15pc, and that of Cha II to be 178+/-18pc. Anexamination of the mean fluxes of T Tauri stars in each cloud providesindependent evidence to suggest that Cha II is significantly moredistant than Cha I. Both clouds appear to be embedded in a macroscopicsheet-like structure extending over much of the Chamaeleon-Musca-Cruxregion. The Chamaeleon III and DC\ts 300.2--16.9 clouds are probablypart of the same structure, with probable distances ~ 140--160pc.
| Optical polarimetry, high--resolution spectroscopy and IR analysis of the Chamaeleon I dark cloud
We present optical polarimetry and high resolution spectroscopy of asample of stars toward the Chamaeleon I dark cloud. We use ourpolarimetry which includes 33 stars to study the wavelength dependenceof the degree and position angle of polarization. From fits to thenormalized wavelength dependence of interstellar polarization, we deriveestimates of lambdaMax ranging from 4500 \AA to 6700 \AA, andPMax ranging from 3 to 8%. The values of lambdaMaxwere found to be well correlated with the IRAS 100 micron intensity,while PMax was found to increase with E_{B-V}. Highresolution spectra of the Ca II, CH, and CH^{+} lines were obtained for10 stars, which show two components of Ca II in absorption at 3.0
| Dust Metamorphosis in the Galaxy
Not Available
| A Study of the Chamaeleon-I Dark Cloud and T-Association - Part Six - Interstellar Polarization Grain Alignment and Magnetic Field
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.268....1W&db_key=AST
| Photometric and spectroscopic analysis of high galactic latitude molecular clouds. II - High-resolution spectroscopic observations of NA I, CA II, CA I, CH, and CH(+1)
High-resolution spectroscopic observations in the wavelengths of thespecies Na I, Ca II, and Ca I and the molecular species CH and CH(+)have been performed toward stars behind a variety of high galacticlatitude molecular clouds (HLCs). Seventeen new detections of molecularabsorption are reported. The sizes, densities, and molecular contentfound for the HLCs are consistent with an interpretation of HLCmolecular cores as extremely compact structures of enhanced molecularcontent which may have evolved from larger H I shells.
| An Einstein Observatory SAO-based catalog of B-type stars
About 4000 X-ray images obtained with the Einstein Observatory are usedto measure the 0.16-4.0 keV emission from 1545 B-type SAO stars fallingin the about 10 percent of the sky surveyed with the IPC. Seventy-fourdetected X-ray sources with B-type stars are identified, and it isestimated that no more than 15 can be misidentified. Upper limits to theX-ray emission of the remaining stars are presented. In addition tosummarizing the X-ray measurements and giving other relevant opticaldata, the present extensive catalog discusses the reduction process andanalyzes selection effects associated with both SAO catalog completenessand IPC target selection procedures. It is concluded that X-rayemission, at the level of Lx not less than 10 exp 30 ergs/s, is quitecommon in B stars of early spectral types (B0-B3), regardless ofluminosity class, but that emission, at the same level, becomes lesscommon, or nonexistent, in later B-type stars.
| The type of variability of Herbig Ae/Be stars
The paper presents a list of 23 Herbig Ae/Be stars and Herbig Ae/Be starcandidates, compiled on the basis of 2 to 8 years of observations in theStromgren photometric system. Results of the study show that spectraltype A0 separates the stars showing large variations in their brightnessfrom stars showing small variations, with the later spectral type starsbeing the more variable. The behavior of the stars in thecolor-magnitude diagram could be divided into three classes: (1) classR, in which there is a monotonic dependence of the color index on visualbrightness, (2) class CR, in which this dependence is not monotonic, and(3) class RB, in which there is no dependence. It was also found thatthe behavior of a star in the color-magnitude diagram is dependent noton the spectral type but on the size of the variation in brightness.
| Long-term photometry of variables at ESO. I - The first data catalogue (1982-1986)
This paper presents the catalog of photometric data in the Stromgrensystem obtained during the first four years (October 1982 - September1986) of the Long-Term Photometry of Variables (LTPV) program at ESO.The data are available in computer-readable form.
| Merged log of IUE observations.
Not Available
| Instrumental effects and the Stroemgren photometric system
The extent to which the use of different photometers can affect resultson stellar color indices was investigated by simultaneously observing asample of widely different stars with several uvby photometric systemsavailable at the ESO, La Silla, Chile. In one instance, the ESO 50-cmtelescope and the four-channel photometer at the Danish 50-cm telescopewere used simultaneously. The reductions were performed separately oneach data set, using a linear color transformation procedure. Theresults agree with theoretical investigations which showed thatsubstantial errors can arise from the nonconformity of passbands. It isemphasized that it is necessary to use separate color transformationsfor various stellar types and classes and for different interstellarreddenings.
| A study of the Chamaeleon dark cloud and T-association. I - Extinction, distance and membership
The results of an observing program to investigate the nature and degreeof reddening of a number of stars in the field towards the dark cloudand T-association in Chamaeleon are presented. The observations compriseoptical (UBVRI) and infrared (JHK) photometry, and optical spectroscopy.New and previously published data are combined to assess membershipcriteria for 110 stars, and separate catalogues of association membersand field stars are presented. Optical identifications are listed for 27IRAS point sources in the region. The reddening/distance relation forfield stars indicates a distance to the cloud of 140 + or - 12 pc. Thisresult confirms that the extinction law is anomalous towards some starsin the cloud, notably the embedded A0 ZAMS star HD 97300, with values ofup to 5.5 for the ratio of total-to-selective extinction. A comparisonof 21-cm data with the reddening of background field stars indicatesthat the ratio N(H I)/E(B-V) is significantly less than the interstellarmean, indicating that most of the hydrogen in the cloud is molecular.
| The ratio of total-to-selective extinction in the Chamaeleon T1 and R Coronae Australis dark clouds
The ratio of total-to-selective extinction, R = A(V)/E(B-V), in the ChaT1 and R CrA dark clouds is investigated via observations of backgroundfield stars seen through these clouds. The observations consist of UBVRIand JHKL photometry as well as classification spectrograms and yieldindividual R values by the color difference method. R is found to beessentially normal in the outer parts of the Cha T1 dark cloud, butseveral stars near the opaque core of this cloud show evidence ofanomalous extinction with R greater than 4. In the R CrA dark cloud, Rincreases with depth into the cloud and reaches clearly anomalous valuesof about 5 for lines of sight with A(V) = 3 mag. The results providefurther evidence for anomalous interstellar extinction laws in somedense interstellar clouds.
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