- ID:
- ivo://CDS.VizieR/J/A+A/445/69
- Title:
- JHK' photometry of C stars in NGC 147
- Short Name:
- J/A+A/445/69
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Near-infrared J, H and K' images were used to investigate the stellar contents of the asymptotic giant branch (AGB) population in the nearby dwarf elliptical galaxy NGC 147. The obtained (K,J-K) and (K,H-K) color-magnitude diagrams contain stars of AGB and red giant branch populations, where the former consists of a group of bright blue stars, a dominant population of M giant and a red C star population.We identified 91 AGB C stars in NGC 147 with the mean absolute magnitude and colors of <M_K_>=-7.56, <(J-K)_0_>=1.81 and <(H-K)_0_>=0.74. The estimated number ratio of C stars to M giant stars (C/M) is 0.16+/-0.02. The estimated local C/M ratios of 0.14+/-0.02 for the inner region (r<70") and 0.19+/-0.03 for the outer region (r>70") indicate a weak radial gradient. The mean bolometric magnitude of 91 C stars in NGC 147 is <M_bol_>=-4.32+/-0.49. The bolometric luminosity function of M giant stars in NGC 147 extends up to M_bol_=-5.8 magnitude, and that of only C stars spans -5.6<M_bol_<-3.5. The color histograms of AGB stars in (J-K) and (H-K) show a main peak containing M giant stars, a red tail containing C stars with a weak excess, and a blue excess possibly due to bright blue foreground stars and AGB stars younger than M giants. The comparison of the theoretical isochrone models with the color distribution and the brightness of AGB stars indicates that most of the bright M giants in NGC 147 were formed at log(t_yr_)~8.4 with a range of 8.2~8.6. Ages of the majority of M giant stars in NGC 147 are similar to those of younger M giant stars in its companion NGC 185, while their formation occurred more recently than the older M giant stars in NGC 185 by ~2Gyrs.
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- ID:
- ivo://CDS.VizieR/J/A+A/456/905
- Title:
- JKs, i'g'r' photometry of C stars in NGC 6822
- Short Name:
- J/A+A/456/905
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From a 2{deg}x2{deg} survey of NGC 6822 we have previously established that this Local Group dwarf irregular galaxy possesses a huge spheroid having more than one degree in length. This spheroid is in rotation but its rotation curve is known only within ~15' from the center. It is therefore critical to identify bright stars belonging to the spheroid to characterize, as far as possible, its outer kinematics. We use the new wide field near infrared imager CPAPIR, operated by the SMARTS consortium, to acquire J, K_s_ images of two 34.8'x34.8' areas in the outer spheroid to search for C stars. The colour diagram of the fields allows the identification of 192 C stars candidates but a study of the FWHM of the images permits the rejection of numerous non-stellar objects with colours similar to C stars. We are left with 75 new C stars, their mean K_s_ magnitude and mean colour are similar to the bulk of known NGC 6822 C stars. This outer spheroid survey confirms that the intermediate-age AGB stars are a major contributor to the stellar populations of the spheroid. The discovery of some 50 C stars well beyond the limit of the previously known rotation curve calls for a promising spectroscopic follow-up to a major axis distance of 40'.
- ID:
- ivo://CDS.VizieR/J/A+A/474/35
- Title:
- JKs photometry of C stars in IC10 and WLM
- Short Name:
- J/A+A/474/35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The selection of AGB C and M stars from NIR colours has been done in recent years using adjustable criteria that are in needs of standardization if one wants to compare, in a coherent manner, properties of various populations. We intend to assess the NIR colour technique to identify C and M stars. We compare the NIR colours of several C stars previously identified from spectroscopy or narrow band techniques in WLM, IC 10 and NGC 6822. We demonstrate that very few M stars have (J-K)_0_>1.4 but a non negligible number of C stars are bluer than this limit. Thus, counts of M and C stars based on such limit do not produce pure samples. C/M ratios determined from NIR colours must be regarded as underestimates mainly because the M numbers include many warm C stars and also K stars if no blue limit is considered.
- ID:
- ivo://CDS.VizieR/J/A+A/493/1075
- Title:
- JKs photometry of C stars in 2 nearby galaxies
- Short Name:
- J/A+A/493/1075
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Thousands of C stars have been identified in Local Group galaxies using narrow band photometry. To survey C stars at larger distances and alternative to the narrow-band approach is needed. We obtain, from ESO Archive data, NIR magnitudes and colours of previously known C stars in two dwarf irregular Local Group galaxies, namely IC 1613 and NGC 3109. We compare the NIR magnitudes and colours of the C star populations, previously identified from narrow band techniques to estimate the star formation history of their intermediate-age populations.
- ID:
- ivo://CDS.VizieR/J/A+A/466/501
- Title:
- JKs photometry of WLM galaxy carbon stars
- Short Name:
- J/A+A/466/501
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We identify the rich carbon star population of the Magellanic-type dwarf irregular galaxy WLM (Wolf-Lundmark-Melotte) and study its photometric properties from deep near-IR observations. The galaxy also exhibits a clear presence of oxygen-rich population. We derive a carbon to M-star ratio of C/M=0.56+/-0.12, relatively high in comparison with many galaxies. The spatial distribution of the AGB stars in WLM hints at the presence of two stellar complexes with a size of a few hundred parsecs. Using the HI map of WLM and the derived gas-to-dust ratio for this galaxy N(HI)/E(B-V)=60+/-10[10^21^at/cm^2^/mag] we re-determined the distance modulus of WLM from the IR photometry of four known Cepheids, obtaining (m-M)0=24.84+/-0.14mag. In addition, we determine the scale length of 0.75+/-0.14kpc of WLM disk in the J-band.
- ID:
- ivo://CDS.VizieR/J/MNRAS/341/534
- Title:
- J-type carbon stars in LMC
- Short Name:
- J/MNRAS/341/534
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A sample of 1497 carbon stars in the Large Magellanic Cloud (LMC) has been observed in the red part of the spectrum with the 2dF facility on the Anglo-Australian Telescope. Of these, 156 have been identified as J-type (i.e. ^13^C-rich) carbon stars using a technique which provides a clear distinction between J stars and the normal N-type carbon stars that comprise the bulk of the sample, and yields few borderline cases. A simple two-dimensional classification of the spectra, based on their spectral slopes in different wavelength regions, has been constructed and found to be related to the more conventional c and j indices, modified to suit the spectral regions observed. Most of the J stars form a photometric sequence in the K-(J-K) colour-magnitude diagram, parallel to and 0.6mag fainter than the N-star sequence. A subset of the J stars (about 13 per cent) are brighter than this J-star sequence; most of these are spectroscopically different from the other J stars. The bright J stars have stronger CN bands than the other J stars and are found strongly concentrated in the central regions of the LMC. Most of the rather few stars in common with Hartwick and Cowley's sample (1988ApJ...334..135H) of suspected CH stars are J stars. Overall, the proportion of carbon stars identified as J stars is somewhat lower than has been found in the Galaxy. The Na D lines are weaker in the LMC J stars than in either the Galactic J stars or the LMC N stars, and do not seem to depend on temperature.
- ID:
- ivo://CDS.VizieR/J/A+AS/122/507
- Title:
- Kinematics of SMC carbon stars
- Short Name:
- J/A+AS/122/507
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a radial velocity survey of a sample of the field population of carbon stars in the outer parts of the Small Magellanic Cloud (SMC). This first set of results includes radial velocities for 71 carbon stars, with an individual precision of +/-2-5km/s. The mean heliocentric velocity of the stars (excluding one very high velocity star) is 149.3+/-3.0km/s with a velocity dispersion of 25.2+/-2.1km/s. These values drop to 145.5+/-2.7km/s and 20.6+/-1.9km/s respectively, if we exclude the stars belonging to the Outer Wing. The velocity distribution does not show the multiple peaks seen in some samples of Population I objects. The mass of the SMC as inferred from the above velocity dispersion (without the outer Wing stars) is =~1.2x10^9^M_{sun}_.
- ID:
- ivo://CDS.VizieR/J/A+AS/102/361
- Title:
- Li abundances in galactic C-stars
- Short Name:
- J/A+AS/102/361
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The equivalent widths and abundances of Lithium in galactic carbon stars are presented in Table 1. The observations were made during 1990 and 1991 in 3 different observatories: Roque de los Muchachos and Calar Alto (Spain), and La Silla (Chile). The resolving power of the spectra is 15000-2000 for the spanish observations, and about 60000 for the stars observed at La Silla.
- ID:
- ivo://CDS.VizieR/J/A+A/403/943
- Title:
- Mass-loss rates of galactic AGB stars
- Short Name:
- J/A+A/403/943
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We are using the 2002 data-release from the Japanese space experiment IRTS to investigate the spatial distribution of galactic mass-losing (>2x10^-8_M_{sun}_/yr) AGB stars and the relative contribution of C-rich and O-rich ones to the replenishment of the ISM. Our sample contains 126 C-rich and 563 O-rich sources which are sorted on the basis of the molecular bands observed in the range 1.4-4.0{mu}m, and for which we estimate distances and mass loss rates from near-infrared photometry (K and L'). There is a clear dependence on galactocentric distance, with O-rich sources outnumbering C-rich ones for {tau}_GC_<8kpc, and the reverse for {tau}_GC_>10kpc. The contribution to the replenishment of the ISM by O-rich AGB stars relative to C-rich ones follows the same trend. Although they are rare (~10% in our sample), sources with 10^-6^M_{sun}_/yr<dM/dt<10^-5^M_{sun}_/yr dominate the replenishment of the ISM by contributing to ~50% of the total of the complete sample. We find 2 carbon stars at more than 1kpc from the Galactic Plane, that probably belong to the halo of our Galaxy.
- ID:
- ivo://CDS.VizieR/J/AJ/142/188
- Title:
- Metal-poor stars from the HES using CH G-band
- Short Name:
- J/AJ/142/188
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe a new method to search for metal-poor candidates from the Hamburg/ESO objective-prism survey (HES) based on identifying stars with apparently strong CH G-band strengths for their colors. The hypothesis we exploit is that large overabundances of carbon are common among metal-poor stars, as has been found by numerous studies over the past two decades. The selection was made by considering two line indices in the 4300{AA} region, applied directly to the low-resolution prism spectra. This work also extends a previously published method by adding bright sources to the sample. The spectra of these stars suffer from saturation effects, compromising the index calculations and leading to an undersampling of the brighter candidates. A simple numerical procedure, based on available photometry, was developed to correct the line indices and overcome this limitation. Visual inspection and classification of the spectra from the HES plates yielded a list of 5288 new metal-poor (and by selection, carbon-rich) candidates, which are presently being used as targets for medium-resolution spectroscopic follow-up. Estimates of the stellar atmospheric parameters, as well as carbon abundances, are now available for 117 of the first candidates, based on follow-up medium-resolution spectra obtained with the SOAR 4.1m and Gemini 8m telescopes. There are eight newly discovered stars with [Fe/H] < -3.0 in our sample, including two with [Fe/H] < -3.5.
