Deep IV-N and Yellow-Red Spectral Surveys for Carbon Stars

Astronomical Journal, 2004

A search of more than 3,000 square degrees of high latitude sky by the Sloan Digital Sky Survey has yielded 251 faint high-latitude carbon stars (FHLCs), the large majority previously uncataloged. We present homogeneous spectroscopy, photometry, and astrometry for the sample. The objects lie in the 15.6 < r < 20.8 range, and exhibit a wide variety of apparent photospheric temperatures, ranging from spectral types near M to as early as F. Proper motion measurements for 222 of the objects show that at least 50%, and quite probably more than 60%, of these objects are actually low luminosity dwarf carbon (dC) stars, in agreement with a variety of recent, more limited investigations which show that such objects are the numerically dominant type of star with C_2 in the spectrum. This SDSS homogeneous sample of ~110 dC stars now constitutes 90% of all known carbon dwarfs, and will grow by another factor of 2-3 by the completion of the Survey. As the spectra of the dC and the faint halo giant C stars are very similar (at least at spectral resolution of 1,000) despite a difference of 10 mag in luminosity, it is imperative that simple luminosity discriminants other than proper motion be developed. We use our enlarged sample of FHLCs to examine a variety of possible luminosity criteria, including many previously suggested, and find that, with certain important caveats, JHK photometry may segregate dwarfs and giants.

2006

No. 7] Spectroscopic Analysis in One-Micron Region 535 *' The identification table of them and the description of detailed results in this study will be published elsewhere very soon. No. 7] Spectroscopic Analysis in One-Micron Region 539

Publications of the Astronomical Society of Japan, 2007

ABSTRACT

Symposium - International Astronomical Union, 1999

The application of multi-object instruments to nearby galaxies permits the spectroscopy of large samples of faint stars. Such data are needed to determine the kinematics and metallicity distributions of stellar systems, to complement the excellent photometric data now becoming available. Together, these data should reveal the star formation and evolutionary histories of Local Group galaxies. The Two-degree Field (2dF) instrument on the Anglo-Australian Telescope is described and some initial results are presented for a sample of 700 carbon stars in the Large Magellanic Cloud. The velocity precision is more than adequate for kinematic studies, while the application of Principal Component Analysis techniques promises to yield an objective and quantitative classification scheme for carbon stars. This may lead to a better understanding of the carbon stars themselves, as well as enhancing their use as tracers of the intermediate-age and old stellar populations. Another application of mul...

Astronomy and …, 1998

We present JHKL photometry of a sample of 150 IRAS stars in the third and fourth galactic quadrant with |b| <2 • selected according to their IRAS colour (0.160≤[12-25]≤1.156). We identify 27 carbon star candidates using the [12-25] vs. K-L two-colour diagram method. Among them, 10 are listed in the Stephenson's catalogue of carbon stars and 17 are new infrared carbon stars (IRCS) candidates. Their distances are found to be larger than 3 kpc. These data are combined with previous data to study the space distribution of IRCS. The number density seems to be independent of the galactocentric distance (R) toward the Galactic Center and to decrease exponentially toward the anticenter. At the present stage, it is not possible to disentangle effects such as incompleteness of the sample, different space distribution law and dependence of the luminosity on metallicity. In particular, we suggest that the apparent scarcity of IRCS in the central direction of the Galaxy (R<5 kpc) might be due to a selection effect. From the available data, we have found no IRCS within 1 kpc of the Galactic Center.

2003

A preliminary analysis of the data from the MSX space infrared satellite, seems to confirm that the [8.8]-[12.5] micron color index is well correlated with the mass-loss rates in carbon stars of our Galaxy. The extension of this midinfrared observation criterion to the Magellanic Clouds, with a small-size telescope like IRAIT, able to perform a continuous survey from Dome-C on the Antarctic Plateau, could be crucial to trace the local AGB population and evolution.

Monthly Notices of the Royal Astronomical Society, 2000

1 D epartm ent of P hysics, K eel e U niversity,K eel e, Sta ordshire, ST 5 5B G , U K 2 Institute of A stronom y, M adingl ey R oad, C am bridge C B 3 1H A , U K 3 South A frican A stronom icalO bservatory, P .O . B ox 9, 7935 O bservatory, S. A frica D raft version A B ST R A C T W e presentproperm oti on m easurem ents forcarbon starsfound duri ng the A PM Survey forC oolC arbon Starsi n the G al acti c H al o (Totten & Irw i n,1998).M easurem ents are obtai ned usi ng a com bi nati on ofPO SSI,PO SSII and U K ST survey pl ates suppl em ented w here necessary by C C D fram es taken at the Isaac N ew ton Tel escope. W e nd no si gni cant proper m oti on for any ofthe new A PM col our-sel ected carbon stars and so concl ude that there are no dwarfcarbon stars present w i thi n thi s sampl e.W e al so present proper m oti on m easurem ents for three previ ousl y know n dwarf carbon stars and dem onstrate that these m easurem ents agree favourabl y w i th those previ ousl y quoted i n the l i terature,veri fyi ng our m ethod ofdeterm i ni ng proper m oti ons. R esul ts from a com pl i m entary program of JH K photom etry obtai ned at the South A fri can A stronom i calO bservatory are al so presented.D warfcarbon stars are bel i eved to have anom al ous near-i nfrared col ours,and thi s feature i s used for further i nvesti gati on of the nature of the A PM carbon stars. O ur resul ts support the use ofJH K photom tery as a dwarf/gi ant di scri m i nator and al so rei nforce the concl usi on that none ofthe new A PM -sel ected carbon stars are dwarfs.Fi nal l y,proper m oti on m easurem ents com bi ned w i th extant JH K photom etry are presented for a sam pl e of previ ousl y know n H al o carbon stars, suggesti ng that one of these stars, C LS29, i s l i kel y to be a previ ousl y unrecogni sed dwarfcarbon star. K ey w ords: stars:carbon { stars:surveys { astrom etry:stars { i nfrared:stars c 1997 R A S

The Astrophysical Journal Supplement Series, 2000

The Stephenson objective prism survey contains many stars of apparently early spectral type whose colors imply interstellar extinction values that lie in the key range between those of nearby (8 \ A V \ 30) reddened stars and the Galactic center infrared sources. As part of a wider program to determine the properties of objects in this survey, we present new optical spectroscopy for 45% of the catalog of D440 stars, placing constraints on their spectral types and luminosity classes. Contamination by intrinsically red stars, suggested by previous infrared observations of much smaller subsamples, is shown to be heavy : around 90% of the survey appears to consist of late-type, mostly K and M, stars of luminosity class I, II, or III. We also identify six S stars, one of which has high photospheric lithium abundance. Fifteen highly reddened early-type stars are identiÐed : these have visual extinctions in the range mag, con-6 \ A V \ 16 Ðrming their potential for studies of the interstellar medium.

International Astronomical Union Colloquium, 1995

We are conducting a long-term deep spectral survey to investigate the distribution of Ap and Am stars in selected fields of the Milky Way and in open star clusters of different ages. The spectral survey is based on objective prism spectra obtained with an eight degree prism attached to the 70/98 cm meniscus telescope (f/3, 135 Å mm−1at Hδ) at the Abastumani Observatory. Kodak IIIa-J emulsions hypersensitized by baking in nitrogen gas are used in combination with a 500 Å FWHM filter centered on Hδ. A limiting magnitude ofmB= 14 was reached in an exposure time of 120 m. Study of the objective prism plates is still in a very early stage. Observations of the central part of the same field taken with a CCD resulted in a limiting magnitudemB= 16. On the basis of spectral material obtained, a wide range of spectra may be classified in the MK system.

Transactions of the International Astronomical Union

With an increasing wealth of data and analyses, as well as growing new areas of interest (such as spectral profiles for the search of extrasolar planets), it is no longer possible to present a comprehensive review on the area of Stellar Spectroscopy. As already stressed by the two predecessors as presidents of this Commission, Drs. D.L. Lambert and M.S. Bessell, the Astronomy…

Proceedings of the International Astronomical Union

Most oxygen-rich late-type giant stars show evidence for chromospheres in their visual spectra (e.g. Call Η & Κ emission features). Cool (i.e. N-type) non-Mira carbon stars, however, have never been observed to have chromospheric emission in their Call Η & Κ lines. However, faint Mgll h & k lines were detected in emission in low-dispersion IUE spectra of the brightest cool carbon stars in the early 1980s. May 1984 saw the first (and only) successful high-dispersion IUE spectrum taken of a cool carbon star, TX Psc (NO; C6,2). Armed with this high-dispersion spectrum, as well as low-dispersion IUE and ground-based spectra, Luttermoser et al. (1989) made the first detailed attempt to semiempirically model the chromosphere of a cool carbon star. This model was successful in reproducing the Mgll lines, but it was not well constrained due to the lack of other observed high-resolution chromospheric profiles for comparison. Modeling carbon star chromospheres can now be addressed more accurately with HST/GHRS high-resolution spectra. New fluoresced emission features have been discovered in the GHRS spectra of carbon stars that are not present in their oxygen-rich counterparts.

Astronomy and Astrophysics Supplement Series, 1997

In this work we present spectroscopic observations centered in the spectral lines most widely used as optical indicators of chromospheric activity (Hα, Hβ, Ca ii H & K, and He i D3) in a sample of F, G, K and M chromospherically inactive stars. The spectra have been obtained with the aim of providing a library of high and mid-resolution spectra to be used in the application of the spectral subtraction technique to obtain the activechromosphere contribution to these lines in chromospherically active single and binary stars. This library can also be used for spectral classification purposes. A digital version with all the spectra is available via ftp and the World Wide Web (WWW) in both ASCII and FITS formats

Astron Astrophys, 2001

We present a hydrostatic analysis of five carbon rich stars, BH Cru, T Cae, S Cen, RU Pup and Y Hya in the wavelength range between 0.5 and 2.5 µm. All except BH Cru, which is a Mira star, show only modest variability. We identify the absorption features of the molecules CO, CN and C2. The overall energy distribution, which is very sensitive to the effective temperature in the investigated wavelength range, as well as the bands of these molecules put strict limits on the possible values of effective temperature and C/O. We show that our model atmospheres and corresponding synthetic spectra are able to reproduce the observed spectra quite accurately from about 0.7 to 2.5 µm. The discrepancies are mainly due to uncertainties in the molecular input data. We discuss briefly why the variations of the molecular features are small and why dynamic phenomena do not play a very important role in this wavelength range. We identify colour indices based on commonly available filters and potentially suitable for the empirical determination of fundamental parameters of carbon stars.

We present a hydrostatic analysis of five carbon rich stars, BH Cru, T Cae, S Cen, RU Pup and Y Hya in the wavelength range between 0.5 and 2.5μm. All except BHCru, which is a Mira star, show only modest variability. We identify the absorption features of the molecules CO, CN and C2. The overall energy distribution, which is very sensitive to the effective temperature in the investigated wavelength range, as well as the bands of these molecules put strict limits on the possible values of effective temperature and C/O. We show that our model atmospheres and corresponding synthetic spectra are able to reproduce the observed spectra quite accurately from about 0.7 to 2.5μm. The discrepancies are mainly due to uncertainties in the molecular input data. We discuss briefly why the variations of the molecular features are small and why dynamic phenomena do not play a very important role in this wavelength range. We identify colour indices based on commonly available filters and potentially suitable for the empirical determination of fundamental parameters of carbon stars.

The Astrophysical Journal, 2013

Among stars showing carbon molecular bands (C stars), the main sequence dwarfs, likely in post-mass transfer binaries, are numerically dominant in the Galaxy. Via spectroscopic selection from the Sloan Digital Sky Survey, we retrieve 1220 C stars, ∼5 times more than previously known, including a wider variety than past techniques such as color or grism selection have netted, and additionally yielding 167 DQ white dwarfs. Of the C stars with proper motion measurements, we identify 69% as clearly dwarfs (dCs), while ∼7% are giants. The dCs likely span absolute magnitudes M i from ∼6.5 to 10.5. "G-type" dC stars with weak CN and relatively blue colors are probably the most massive dCs still cool enough to show C 2 bands. We report Balmer emission in 22 dCs, none of which are G-types. We find 8 new DA/dC stars in composite spectrum binaries, quadrupling the total sample of these "smoking guns" for AGB binary mass transfer. Eleven very red C stars with strong red CN bands appear to be "N"-type AGB stars at large Galactocentric distances, one likely a new discovery in the dIrr galaxy Leo A. Two such stars within 30 ′ of each other may trace a previously unidentified dwarf galaxy or tidal stream at ∼40 kpc. We explore the multiwavelength properties of the sample and report the first X-ray detection of a dC star, which shows strong Balmer emission. Our own spectroscopic survey additionally provides the dC surface density from a complete sample of dwarfs limited by magnitude, color, and proper-motion.