- ID:
- ivo://CDS.VizieR/J/AJ/121/169
- Title:
- Imaging and spectroscopy of Tol 1214-277
- Short Name:
- J/AJ/121/169
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectrophotometric study based on VLT/FORS I observations of one of the most metal-deficient blue compact dwarf (BCD) galaxies known, Tol 1214-277 (Z~Zsolar/25). The data show that roughly half of the total luminosity of the BCD originates from a bright and compact starburst region located at the northeastern tip of a faint dwarf galaxy with cometary appearance. The starburst has ignited less than 4 Myr ago and its emission is powered by several thousand O7V stars and ~170 late-type nitrogen Wolf-Rayet stars located within a compact region with <~500pc in diameter. For the first time in a BCD, a relatively strong [Fe V] {lambda}4227 emission line is seen which together with intense He II {lambda}4686 emission indicates the presence of a very hard radiation field in Tol 1214-277. We argue that this extraordinarily hard radiation originates from both Wolf-Rayet stars and radiative shocks in the starburst region. The structural properties of the low surface brightness (LSB) component underlying the starburst have been investigated by means of surface photometry down to 28 B mag.arcsec^-2^. We find that, for a surface brightness level fainter than ~24.5 B mag.arcsec^-2^, an exponential fitting law provides an adequate approximation to its radial intensity distribution. The broadband colors in the outskirts of the LSB component of Tol 1214-277 are nearly constant and are consistent with an age below one Gyr. This conclusion is supported by the comparison of the observed spectral energy distribution (SED) of the LSB host with theoretical SEDs.
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- ID:
- ivo://CDS.VizieR/J/AJ/138/1003
- Title:
- IR photometry of massive LMC stars
- Short Name:
- J/AJ/138/1003
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of 1750 massive stars in the Large Magellanic Cloud (LMC), with accurate spectral types compiled from the literature, and a photometric catalog for a subset of 1268 of these stars, with the goal of exploring their infrared properties. The photometric catalog consists of stars with infrared counterparts in the Spitzer SAGE survey database, for which we present uniform photometry from 0.3 to 24um in the UBVIJHKs+IRAC+MIPS24 bands. The resulting infrared color-magnitude diagrams illustrate that the supergiant B[e], red supergiant, and luminous blue variable (LBV) stars are among the brightest infrared point sources in the LMC, due to their intrinsic brightness, and at longer wavelengths, due to dust. We detect infrared excesses due to free-free emission among ~900 OB stars, which correlate with luminosity class. We confirm the presence of dust around 10 supergiant B[e] stars, finding the shape of their spectral energy distributions (SEDs) to be very similar, in contrast to the variety of SED shapes among the spectrally variable LBVs. The similar luminosities of B[e] supergiants (log L/L_{sun}_>=4) and the rare, dusty progenitors of the new class of optical transients (e.g., SN 2008S and NGC 300 OT), plus the fact that dust is present in both types of objects, suggests a common origin for them. We find the infrared colors for Wolf-Rayet stars to be independent of spectral type and their SEDs to be flatter than what models predict.
- ID:
- ivo://CDS.VizieR/J/AJ/140/416
- Title:
- IR photometry of massive stars in the SMC
- Short Name:
- J/AJ/140/416
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of 5324 massive stars in the Small Magellanic Cloud (SMC), with accurate spectral types compiled from the literature, and a photometric catalog for a subset of 3654 of these stars, with the goal of exploring their infrared properties. The photometric catalog consists of stars with infrared counterparts in the Spitzer SAGE-SMC survey database, for which we present uniform photometry from 0.3 to 24um in the UBVIJHKs+IRAC+MIPS24 bands.
- ID:
- ivo://CDS.VizieR/J/A+AS/108/669
- Title:
- IUE spectra of WR stars
- Short Name:
- J/A+AS/108/669
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/A+A/584/A2
- Title:
- KMOS view of the Galactic centre. I.
- Short Name:
- J/A+A/584/A2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Galactic centre hosts a crowded, dense nuclear star cluster with a half-light radius of 4pc. Most of the stars in the Galactic centre are cool late-type stars, but there are also >=100 hot early-type stars in the central parsec of the Milky Way. These stars are only 3-8Myr old. Our knowledge of the number and distribution of early-type stars in the Galactic centre is incomplete. Only a few spectroscopic observations have been made beyond a projected distance of 0.5pc of the Galactic centre. The distribution and kinematics of early-type stars are essential to understand the formation and growth of the nuclear star cluster.
- ID:
- ivo://CDS.VizieR/J/MNRAS/324/33
- Title:
- MC WC/WO stars - Colliding winds
- Short Name:
- J/MNRAS/324/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Files br22rv.dat, br31rv.dat, br32rv.dat, ab8rv.dat, wr9rv.dat and wr30arv.dat contain spectroscopic radial velocity data of six Magellanic Cloud WC/WO class binary Wolf-Rayet stars. The data are derived from the C IV 5808{AA} emission line and the He II 5412{AA} absorption line. The data were obtained during one mission in 1984 at CTIO and two missions in 1993 at CASLEO.
- ID:
- ivo://CDS.VizieR/J/A+A/625/A132
- Title:
- Models for massive stars in the SMC
- Short Name:
- J/A+A/625/A132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The evolution of massive stars is strongly influenced by internal mixing processes such as semiconvection, convective core overshooting, and rotationally induced mixing. None of these processes are currently well constrained. We investigate models for massive stars in the Small Magellanic Cloud (SMC), for which stellar-wind mass loss is less important than for their metal-rich counterparts. We aim to constrain the various mixing efficiencies by comparing model results to observations. For this purpose, we use the stellar-evolution code MESA to compute more than 60 grids of detailed evolutionary models for stars with initial masses of 9...100M_{sun}_, assuming different combinations of mixing efficiencies of the various processes in each grid. Our models evolve through core hydrogen and helium burning, such that they can be compared with the massive main sequence and supergiant population of the SMC. We find that for most of the combinations of the mixing efficiencies, models in a wide mass range spend core-helium burning either only as blue supergiants, or only as red supergiants. The latter case corresponds to models that maintain a shallow slope of the hydrogen/helium (H/He) gradient separating the core and the envelope of the models. Only a small part of the mixing parameter space leads to models that produce a significant number of blue and red supergiants, which are both in abundance in the SMC. Some of our grids also predict a cut-o in the number of red supergiants above logL/L_{sun}_=5...5.5. Interestingly, these models contain steep H/He gradients, as is required to understand the hot, hydrogen-rich Wolf-Rayet stars in the SMC. We find that unless it is very fast, rotation has a limited effect on the H/He profiles in our models. While we use specific implementations of the considered mixing processes, they comprehensively probe the two firstorder structural parameters, the core mass and the H/He gradient in the core-envelope interface. Our results imply that in massive stars, mixing during the main-sequence evolution leads to a moderate increase in the helium core masses, and also that the H/He gradients above the helium cores become very steep. Our model grids can be used to further refine the various mixing efficiencies with the help of future observational surveys of the massive stars in the SMC, and thereby help to considerably reduce the uncertainties in models of massive star evolution.
- ID:
- ivo://CDS.VizieR/J/ApJS/252/21
- Title:
- Multiwavelength survey of WR stars in LMC
- Short Name:
- J/ApJS/252/21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Surveys of Wolf-Rayet (WR) stars in the Large Magellanic Cloud (LMC) have yielded a fairly complete catalog of 154 known stars. We have conducted a comprehensive, multiwavelength study of the interstellar/circumstellar environments of WR stars, using the Magellanic Cloud Emission Line Survey images in the H{alpha}, [OIII], and [SII] lines; Spitzer Space Telescope 8 and 24{mu}m images; Blanco 4m Telescope H{alpha} CCD images; and Australian Telescope Compact Array + Parkes Telescope HI data cube of the LMC. We have also examined whether the WR stars are in OB associations, classified the HII environments of WR stars, and used this information to qualitatively assess the WR stars' evolutionary stages. The 30 Dor giant HII region has active star formation and hosts young massive clusters, thus we have made statistical analyses for 30 Dor and the rest of the LMC both separately and altogether. Due to the presence of massive young clusters, the WR population in 30 Dor is quite different from that from elsewhere in the LMC. We find small bubbles (<50pc diameter) around ~12% of WR stars in the LMC, most of which are WN stars and not in OB associations. The scarcity of small WR bubbles is discussed. Spectroscopic analyses of abundances are needed to determine whether the small WR bubbles contain interstellar medium or circumstellar medium. Implications of the statistics of interstellar environments and OB associations around WR stars are discussed. Multiwavelength images of each LMC WR star are presented.
- ID:
- ivo://CDS.VizieR/J/ApJ/789/10
- Title:
- M33 WR and Of-type Stars
- Short Name:
- J/ApJ/789/10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Massive star evolutionary models generally predict the correct ratio of WC-type and WN-type Wolf-Rayet stars at low metallicities, but underestimate the ratio at higher (solar and above) metallicities. One possible explanation for this failure is perhaps single-star models are not sufficient and Roche-lobe overflow in close binaries is necessary to produce the "extra" WC stars at higher metallicities. However, this would require the frequency of close massive binaries to be metallicity dependent. Here we test this hypothesis by searching for close Wolf-Rayet binaries in the high metallicity environments of M31 and the center of M33 as well as in the lower metallicity environments of the middle and outer regions of M33. After identifying ~100 Wolf-Rayet binaries based on radial velocity variations, we conclude that the close binary frequency of Wolf-Rayets is not metallicity dependent and thus other factors must be responsible for the overabundance of WC stars at high metallicities. However, our initial identifications and observations of these close binaries have already been put to good use as we are currently observing additional epochs for eventual orbit and mass determinations.
- ID:
- ivo://CDS.VizieR/J/ApJ/505/793
- Title:
- New WR star in M33
- Short Name:
- J/ApJ/505/793
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We expect the evolution of massive stars to be strongly influenced by mass loss and hence to be sensitive to metallicity. It should be possible to test this "Conti scenario" be comparing the populations of evolved massive stars among the Local Group galaxies, but such investigations have been hampered by incompleteness. In a previous paper, we presented results of a new survey for red supergiants (RSGs) in selected regions of the Local Group galaxies M33, M31, and NGC 6822. In the present paper, we survey eight fields in M33 for Wolf-Rayet stars (WRs), using interference-filter imaging with a CCD to select candidates. Follow-up spectroscopy is used to confirm 22 newly found WR stars, 21 of WN type. We establish that our survey would readily detect WRs as weak-lined as any known, and we conclude that our survey is essentially complete.
