Search

We have studied several color-color infrared diagrams of the 276 late type stars of the BIS catalog. For 95 of these stars we derived spectral classification from our slit spectroscopy. From the 2MASS color diagram we derive that none of the sample stars is a dwarf. The WISE 3.4-12 vs 12-22 plot is the best to discriminate the variability type (Mira, irregular and not-variable), as well as Carbon stars: IRAS colors are less useful due to the poor quality of the data for most of the BIS stars. Mixed plots involving 2MASS, AKARI and WISE were also explored: the 2MASS-AKARI J-[S09] vs [S09]-[L18] plot is efficient to discriminate Carbon and Mira stars. From the color plots and our spectroscopy we can statistically predict that in whole BIS catalog no other dusty Carbon star is present, while a few Miras and CH or R Carbon stars could be discovered. Only about 15 percent of the BIS stars are of early M type., Comment: 14 pages, 5 figures, accepted for publication in Revista Mexicana de Astronom{\i}a y Astrof{\i}sica

Through the analysis and interpretation of newly obtained and of literature data we have clarified the nature of poorly investigated IRAS point sources classified as late type stars, belonging to the Byurakan IRAS ~Stars catalog. From medium resolution spectroscopyof 95 stars we have strongly revised 47 spectral types and newly classified 31 sources. Nine stars are of G or K types, four are N carbon stars in the Asymptotic Giant Branch, the others being M type stars. From literature and new photometric observations we have studied their variability behaviour. For the regular variables we determined distances, absolute magnitudes and mass loss rates. For the other stars we estimated the distances, ranging between 1.3 and 10~kpc with a median of 2.8~kpc from the galactic plane, indicating that BIS stars mostly belong to the halo population., Comment: 28 pages, 3 figures, accepted by Revista Mexicana de Astronomia y Astrofisica

Infra-Red(IR) astronomical databases, namely, IRAS, 2MASS, WISE, and Spitzer, are used to analyze photometric data of 126 carbon stars whose spectra are visible in the First Byurakan Survey low-resolution spectral plates. Among these, six new objects, recently confirmed on the digitized FBS plates, are included. For three of them, moderate-resolution CCD optical spectra are also presented. In this work several IR color-color diagrams are studied. Early and late-type C stars are separated in the JHK Near-Infra-Red(NIR) color-color plots, as well as in the WISE W3-W4 versus W1-W2 diagram. Late N-type Asymptotic Giant Branch stars are redder in W1-W2, while early-types(CH and R giants) are redder in W3-W4 as expected. Objects with W2-W3 > 1.0 mag. show double-peaked spectral energy distribution, indicating the existence of the circumstellar envelopes around them. 26 N-type stars have IRAS Point Source Catalog(PSC) associations. For FBS 1812+455 IRAS Low-Resolution Spectra in the wavelength range 7.7 - 22.6micron and Spitzer Space Telescope Spectra in the range 5 - 38micro are presented clearly showing absorption features of C2H2(acetylene) molecule at 7.5 and 13.7micron , and the SiC(silicone carbide) emission at 11.3micron. The mass-loss rates for eight Mira-type variables are derived from the K-[12] color and from the pulsation periods. The reddest object among the targets is N-type C star FBS 2213+421, which belong to the group of the cold post-AGB R Coronae Borealis(R CrB) variables., Comment: 12 pages, 5 figures

Demers and Battinelli published, in 2007 the rotation curve of the Milky Way based on the radial velocity of carbon stars outside the Solar circle. Since then we have established a new list of candidates for spectroscopy. The goal of this paper is to determine the rotation curve of the galaxy, as far as possible from the galactic center, using N type carbon stars. The stars were selected from their dereddened 2MASS colours, then the spectra were obtained with the Dominion Astrophysical Observatory and Asiago 1.8 meter telescopes. This publication adds radial velocities and Galactrocentric distances of 36 carbon stars, from which 20 are new confirmed. The new results for stars up to 25 kpc from the galactic center, suggest that the rotation curve shows a slight decline beyond the Solar circle., Comment: 13 pages, 3 figures, 1 table; accepted for publication in Astrophysics

Carbon rich stars of Population II, such as CH giants, can provide direct information on the role of low to intermediate mass stars of the Halo in early Galactic evolution. Moreover, accurate knowledge of the CH stellar population is a critical requirement for building up scenarios for early Galactic chemical evolution. The first list of the faint high latitude C stars (FHLCs), found in the Digitized First Byurakan Survey {http://byurakan.phys.uniroma1.it and http://www.aras.am/Dfbs/dfbs.html} (DFBS) is given in a paper recently submitted for publication in Astronomy ad Astrophysics. In the present work, we report the recent discovery of two additional CH type stars (not previously catalogued), namely DFBS J075331.98+190344.3 and DFBS J111422.94+091442.7, detected on the DFBS plates with help of the image analysis softwares (FITSView and SAOImage DS9). Medium resolution spectra confirm the C rich nature for both of them. Using infrared color magnitudes relationship, we estimated the distances and K band absolute magnitudes of the new objects., Comment: 5 pages, 1 figure, Research Note submitted for publication in Astrophysics

Faint high latitude carbon stars are rare objects commonly thought to be distant, luminous giants. For this reason they are often used to probe the structure of the Galactic halo; however more accurate investigation of photometric and spectroscopic surveys has revealed an increasing percentage of nearby objects with luminosities of main sequence stars. Aiming at clarifyin the nature of the ten carbon star candidates present in the General Catalog of the Second Byurakan Survey we analyzed new optical spectra and photometry and used astronomical databases available on the web. We verified that two stars are N-type giants already confirmed by other surveys. We found that four candidates are M type stars and confirmed the carbon nature of the remaining four stars; the characteristics of three of them are consistent with an early CH giant type. The fourth candidate, SBS1310+561 identified with a high proper motion star, is a rare type of dwarf carbon showing emission lines in its optical spectrum. We estimated absolute magnitudes and distances to the dwarf carbon and the three CH stars. Our limited sample confirmed the increasing evidence that spectroscopy or colour alone are not conclusive luminosity discriminants for CH$-$type carbon stars ., Comment: 9 pages, 5 figures, submitted for publication in A&A, research note

The goal of this paper is to present and analyse a new sample of cool carbon (C)stars located in the halo. Twenty three new C stars were discovered. Spectra are typical of N-type stars with C2 and CN bands and sometimes Halpha in emission. ... Four objects are particularly red with J-K > 3, with 2 located at more than 5 kpc. from the Galactic plane. Eight additional objects with similar properties are found in the literature and our previous works. These 12 C stars could be useful to study mass loss at low metallicity. Two objects are at distances of 95 and 110 kpc. They are located in the region with galactocentric Z < -60 kpc in which the model of Law et al. predicts the Sgr stream to have a loop. (Abstact abridged), Comment: 16 pages, 12 figures, accepted by AA

We present new results from an ongoing survey of carbon-rich asymptotic giant (AGB) stars in the halo of our Galaxy. After selecting candidates primarily through their 2MASS colours, slit spectroscopy was achieved at the ESO NTT telescope. Twenty-one new AGB carbon stars were discovered, increasing the total of presently known similar AGB C stars to about 120. A further four were observed again in order to confirm their carbon-rich nature and measure radial velocities. Two main findings emerge from this work. First, we found a C star located at about 130 kpc from the Sun and at b = -62 degrees. This distant star is remarkably close (5 kpc) to the principal plane of the Stream of the Sagittarius dwarf galaxy, and is likely to be a tracer of a distant poorly populated southern warp of the Stream. etc etc, Comment: accepted by Astronomy and Astrophysics

We present the first results of a new survey for finding cool N-type carbon (C) stars in the halo of the Galaxy. Candidates were first selected in the 2MASS Second Incremental Release database with JHKs colours typical of red AGB C stars and Ks < 13, and susequently checked through slit spectroscopy. 27 new halo C stars were discovered, and a detailed study of their properties are given (distance, radial velocity, variablility, proper motion, colors etc). It is found that most probably all these stars are true luminous AGB stars, rather than C dwarfs. It is finally found that about half of these stars belong to the Sgr Stream. (this abstract was shortened), Comment: 21 pages, 12 figs, accepted by Astron. & Astrophysics

We report the discovery of seven hitherto unknown L-dwarfs found as a result of a spectroscopic search for distant AGB stars. Their far-red and near-infrared colours are very similar to known dwarfs of the same spectral type. One new object is among the ~30 brightest L-dwarfs, with K_s=12.12, and is nearby, ~20pc. Using low resolution spectroscopy from the Danish 1.54 m ESO telescope, spectral types in the range L0.5 - L5 are derived for these seven L-dwarfs by direct comparison to L-type standards taken from Kirkpatrick et al. (1999). Distances are determined from existing calibrations, and together with measured proper motions, yield kinematics for the seven new dwarfs consistent with that expected for the solar neighbourhood disk population., Comment: 8 pages, 11 figures, accepted by A&A