- ID:
- ivo://CDS.VizieR/J/AJ/96/1884
- Title:
- BVRJHK photometry of M31 red supergiants
- Short Name:
- J/AJ/96/1884
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have surveyed M31 for its most luminous red stars; 300 candidates were found distributed across the face of the galaxy. JHK infrared photometry was observed for 57 of the candidates, and far-red (6800-8800A) spectra were also obtained for 45 stars. We have used the strength of the Ca II triplet (~8500A) and the J-H and H-K colors as luminosity discriminants to separate the supergiants from the foreground dwarfs. With these criteria, 23 probable late-type supergiants were identified. We discuss their distribution and relative numbers of the red supergiants in comparison with the known WR stars in M31. Accurate extinction and infrared (K=2.2{mu}m) and bolometric luminosities are also derived from the infrared photometry. We find that although visually bright red supergiants (M_V_=-8mag) exist in M31, the most luminous (M_bol_) red supergiants are not found in the relative numbers we would expect in a galaxy of its size and mass. It is probable that the rate of massive-star formation is less in M31, an Sb type spiral, than has been observed in the Sc spirals and irregulars.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/571/A43
- Title:
- Candidate red supergiants in Galactic clusters
- Short Name:
- J/A+A/571/A43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Clear identifications of Galactic young stellar clusters farther than a few kpc from the Sun are rare, despite the large number of candidate clusters. We aim to improve the selection of candidate clusters rich in massive stars with a multiwavelength analysis of photometric Galactic data that range from optical to mid-infrared wavelengths. We present a photometric and spectroscopic analysis of five candidate stellar clusters, which were selected as overdensities with bright stars (K_s_<7mag) in GLIMPSE and 2MASS images. A total of 48 infrared spectra were obtained. The combination of photometry and spectroscopy yielded six new red supergiant stars with masses from 10M_{sun}_ to 15M_{sun}_. Two red supergiants are located at Galactic coordinates (l,b)=(16.7{deg}, -0.63{deg}) and at a distance of about ~3.9kpc; four other red supergiants are members of a cluster at Galactic coordinates (l,b)=(49.3{deg}, +0.72{deg}) and at a distance of ~7.0kpc. Spectroscopic analysis of the brightest stars of detected overdensities and studies of interstellar extinction along their line of sights are fundamental to distinguish regions of low extinction from actual stellar clusters. The census of young star clusters containing red supergiants is incomplete; in the existing all-sky near-infrared surveys, they can be identified as overdensities of bright stars with infrared color-magnitude diagrams characterized by gaps.
- ID:
- ivo://CDS.VizieR/J/A+A/566/L10
- Title:
- Cepheid radial velocity amplitude modulations
- Short Name:
- J/A+A/566/L10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Classical Cepheids are crucial calibrators of the extragalactic distance scale. The Baade-Wesselink technique can be used to calibrate Cepheid distances using Cepheids in the Galaxy and the Magellanic Clouds. To report the discovery of modulations in radial velocity (RV) curves of four Galactic classical Cepheids and to investigate their impact as a systematic uncertainty for Baade-Wesselink distances. Highly precise Doppler measurements were obtained using the Coralie high-resolution spectrograph since 2011. Particular care was taken to sample all phase points in order to very accurately trace the RV curve during multiple epochs and to search for differences in linear radius variations derived from observations obtained at different epochs. Different timescales are sampled, ranging from cycle-to-cycle to months and years. The unprecedented combination of excellent phase coverage obtained during multiple epochs and high precision enabled the discovery of significant modulation in the RV curves of the short-period s-Cepheids QZ Normae and V335 Puppis, as well as the long-period fundamental mode Cepheids l Carinae and RS Puppis. The modulations manifest as shape and amplitude variations that vary smoothly over timescales of years for short-period Cepheids, and from one pulsation cycle to the next in the long-period Cepheids. The order of magnitude of the effect ranges from several hundred m/s to a few km/s. The resulting difference among linear radius variations derived using data from different epochs can lead to systematic errors of up to 15% for Baade-Wesselink-type distances, if the employed angular and linear radius variations are not determined contemporaneously. The different nature of the Cepheids exhibiting modulation in their RV curves suggests that this phenomenon is common. The observational baseline is not yet sufficient to conclude whether these modulations are periodic. In order to ensure the accuracy of Baade-Wesselink distances, angular and linear radius variations should always be determined contemporaneously.
- ID:
- ivo://CDS.VizieR/J/A+A/324/435
- Title:
- Chemical composition of six K supergiants in the SMC
- Short Name:
- J/A+A/324/435
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A sample of six SMC cool stars (K supergiants) are analysed by high resolution spectroscopy in order to investigate their chemical content, which should reflect that of the current interstellar medium within the SMC. The abundance of Na, Al, {alpha}-elements, Fe peak and heavy elements are derived through an LTE analysis of the lines, compared to a Galactic "standard" (the well-studied K giant Arcturus) and discussed in terms of chemical evolution of the SMC. The following results were obtained: 1. All the stars from this sample are metal deficient ([Fe/H] ranges from -0.59 to -0.89dex). The abundance varies little from star-to-star (0.10dex rms, comparable with the expected error due to uncertainties on the effective parameters of the stars), in agreement with the very small chemical composition variations among the H II regions within the SMC found by Pagel et al. (1978MNRAS.184..569P). 2. Sodium is not strongly enhanced in these stars, and the star-to-star scatter is larger than expected. 3. At variance with metal-poor stars in our Galaxy, the so-called {alpha}-elements do not seem to be enhanced. 4. Nickel displays a noticeable depletion with respect to iron ([Ni/Fe]=~-0.3dex), at variance with what is found in the SMC F supergiants and in Arcturus. 5. Except for PMMR 144, the s and r process elements heavier than Ba are enhanced in all of our stars by =~+0.4dex.
- ID:
- ivo://CDS.VizieR/J/MNRAS/414/418
- Title:
- Chromospheric Mg II h+k flux of evolved stars
- Short Name:
- J/MNRAS/414/418
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Of a total of 177 cool G, K and M giants and supergiants, we measured the MgII h+k line emission of extended chromospheres in high-resolution (LWR) International Ultraviolet Explorer (IUE) spectra by using the IUE final data archive at the Space Telescope Science Institute (STScI) and derived the respective stellar surface fluxes. They represent the chromospheric radiative energy losses presumably related to basal heating by the dissipation of acoustic waves, plus a highly variable contribution due to magnetic activity.
- ID:
- ivo://CDS.VizieR/J/MNRAS/451/3504
- Title:
- Classification of IRS sources in the SMC
- Short Name:
- J/MNRAS/451/3504
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Magellanic clouds are uniquely placed to study the stellar contribution to dust emission. Individual stars can be resolved in these systems even in the mid-infrared, and they are close enough to allow detection of infrared excess caused by dust. We have searched the Spitzer Space Telescope data archive for all Infrared Spectrograph (IRS) staring-mode observations of the Small Magellanic Cloud (SMC) and found that 209 Infrared Array Camera (IRAC) point sources within the footprint of the Surveying the Agents of Galaxy Evolution in the Small Magellanic Cloud (SAGE-SMC) Spitzer Legacy programme were targeted, within a total of 311 staring mode observations. We classify these point sources using a decision tree method of object classification, based on infrared spectral features, continuum and spectral energy distribution shape, bolometric luminosity, cluster membership and variability information. We find 58 asymptotic giant branch (AGB) stars, 51 young stellar objects (YSOs), 4 post-AGB objects, 22 Red Supergiants (RSGs), 27 stars (of which 23 are dusty OB stars), 24 planetary nebulae (PNe), 10 Wolf-Rayet (WR) stars, 3 HII regions, 3 R Coronae Borealis (R CrB) stars, 1 Blue Supergiant and 6 other objects, including 2 foreground AGB stars. We use these classifications to evaluate the success of photometric classification methods reported in the literature.
- ID:
- ivo://CDS.VizieR/J/MNRAS/286/500
- Title:
- Classification of Late Type Stars
- Short Name:
- J/MNRAS/286/500
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Energy distributions for 33 galactic (super)giants situated mostly in the southern Milky Way in the range from 4800 to 7700 Angstroems with an effective resolution of 10 Angstroems are presented here. The observations and reductions are described in the paper. The errors of the absolute and relative flux calibration are 0.028 and 0.021 mag, respectively. The S/N ratio is at least 80 for each star. Cross references, MK classifications and spectral indices one may find in the paper. Further informations are available at M.O.Oestreicher (mio@astro.ruhr-uni-bochum.de). The data are given in three files: 1) stars.dat A list of the programme stars listing the HD/HDE numbers, MK types and positions related to J2000 2) absolute.dat A list of absolute fluxes for each star observed under photometric conditions (18 stars). The fluxes are given in magnitudes according to the system of Hayes & Latham (1975). A monochromatic magnitude of 0.00 corresponds to a flux of 3.5x10^-20^ erg.cm-2.s-1.Hz-1, (3.5x10^-23^ W/m2/Hz), i.e. the fluxes are related to FREQUENCY INTERVALS. 3) relative.dat A list of relative fluxes for each star observed in nights of low quality (15 stars). The fluxes are normalized to 1 at 5555 Angstr. and are related to WAVELENGTH INTERVALS.
- ID:
- ivo://CDS.VizieR/J/MNRAS/485/2417
- Title:
- CO J=2-1 NOEMA observations of mu Cep
- Short Name:
- J/MNRAS/485/2417
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Red supergiant stars are surrounded by a gaseous and dusty circumstellar environment created by their mass loss which spreads heavy elements into the interstellar medium. The structure and the dynamics of this envelope are crucial to understand the processes driving the red supergiant mass loss and the shaping of the pre-supernova ejecta. We have observed the emission from the CO J=2-1 line from the red supergiant star {mu} Cep with the NOEMA interferometer. In the line the synthesized beam was 0.92x0.72-arcsec (590x462au at 641pc). The continuum map shows only the unresolved contribution of the free-free emission of the star chromosphere. The continuum-subtracted channel maps reveal a very inhomogeneous and clumpy circumstellar environment. In particular, we detected a bright CO clump, as bright as the central source in the line, at 1.80-arcsec south-west from the star, in the blue channel maps. After a deprojection of the radial velocity assuming two different constant wind velocities, the observations were modelled using the 3D radiative transfer code LIME to derive the characteristics of the different structures. We determine that the gaseous clumps observed around {mu} Cep are responsible for a mass loss rate of (4.9+/-1.0)x10^-7^M_[sun}_/yr, in addition to a spatially unresolved wind component with an estimated mass-loss rate of 2.0x10^-6^M_[sun}_/yr. Therefore, the clumps have a significant role in {mu} Cep's mass loss (>=25%). We cannot exclude that the unresolved central outflow may be made of smaller unresolved clumps.
- ID:
- ivo://CDS.VizieR/J/ApJ/597/323
- Title:
- Cool stars at the Galactic Center
- Short Name:
- J/ApJ/597/323
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present {lambda}/{Delta}{lambda}=550-1200 near-infrared H and K spectra for a magnitude-limited sample of 79 asymptotic giant branch and cool supergiant stars in the central ~5pc (diameter) of the Galaxy. We use a set of similar spectra obtained for solar neighborhood stars with known Teff and Mbol that is in the same range as the Galactic center (GC) sample to derive Teff and Mbol for the GC sample. We then construct the H-R diagram for the GC sample. Using an automated maximum likelihood routine, we derive a coarse star formation history of the GC.
- ID:
- ivo://CDS.VizieR/J/A+A/601/A76
- Title:
- DIRECT lightcurves of 21 luminous YSGs in M33
- Short Name:
- J/A+A/601/A76
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The evolution of massive stars surviving the red supergiant (RSG) stage remains unexplored due to the rarity of such objects. The yellow hypergiants (YHGs) appear to be the warm counterparts of post-RSG classes located near the Humphreys-Davidson upper luminosity limit, which are characterized by atmospheric instability and high mass-loss rates. We aim to increase the number of YHGs in M33 and thus to contribute to a better understanding of the pre-supernova evolution of massive stars. Optical spectroscopy of five dust-enshrouded YSGs selected from mid-IR criteria was obtained with the goal of detecting evidence of extensive atmospheres. We also analyzed BVIc photometry for 21 of the most luminous YSGs in M33 to identify changes in the spectral type. To explore the properties of circumstellar dust, we performed SED-fitting of multi-band photometry of the 21 YSGs. We find three luminous YSGs in our sample to be YHG candidates, as they are surrounded by hot dust and are enshrouded within extended, cold dusty envelopes. Our spectroscopy of star 2 shows emission of more than one H{alpha} component, as well as emission of CaII, implying an extended atmospheric structure. In addition, the long-term monitoring of the star reveals a dimming in the visual light curve of amplitude larger than 0.5mag that caused an apparent drop in the temperature that exceeded 500K. We suggest the observed variability to be analogous to that of the Galactic YHG {rho} Cas. Five less luminous YSGs are suggested as post-RSG candidates showing evidence of hot or/and cool dust emission. We demonstrate that mid-IR photometry, combined with optical spectroscopy and time-series photometry, provide a robust method for identifying candidate YHGs. Future discovery of YHGs in Local Group galaxies is critical for the study of the late evolution of intermediate-mass massive stars.
