- ID:
- ivo://CDS.VizieR/J/ApJ/425/122
- Title:
- IMF from UV stellar photometry
- Short Name:
- J/ApJ/425/122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- UV stellar photometry is presented for 1563 stars within a 40' circular field in the LMC, excluding the 10'x10' field centered on R136 investigated earlier by Hill et al. (1993). Magnitudes are computed from images obtained by the Ultraviolet Imaging Telescope in bands centered at 1615A and 2558A. Stellar masses and extinctions are estimated for the stars in associations using the evolutionary models of Schaerer et al. (1993), assuming the age is 4Myr and that the local LMC extinction follows the Fitzpatrick (1985) 30 Dor extinction curve. The estimated slope of the initial mass function (IMF) for massive stars (>15M_{sun}_) within the Lucke and Hodge (LH) associations is {gamma}=-1.08+/-0.2. Initial masses and extinctions for stars not within LH associations are estimated assuming that the stellar age is either 4Myr or half the stellar lifetime, whichever is larger. The estimated slope of the IMF for massive stars not within LH associations is {gamma}=-1.74+/-0.3 (assuming continuous star formation), compared with {gamma}=-1.35, and {gamma}=-1.7+/-0.5, obtained for the Galaxy by Salpeter (1955) and Scalo (1986), respectively, and {gamma}=-1.6 obtained for massive stars in the Galaxy by Garmany, Conti, & Chiosi (1982). The shallower slope of the association IMF suggests that not only is the star formation rate higher in associations, but that the local conditions favor the formation of higher mass stars there. We make no corrections for binaries or incompleteness.
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- ID:
- ivo://CDS.VizieR/J/AJ/161/206
- Title:
- Infrared imaging of new born cluster H72.97-69.39
- Short Name:
- J/AJ/161/206
- Date:
- 20 Jan 2022
- Publisher:
- CDS
- Description:
- Young massive clusters and super star clusters (SSCs) represent an extreme mode of star formation. Far-infrared imaging of the Magellanic Clouds has identified one potential embedded SSC, HSO-BMHERICC-J72.971176-69.391112 (H72.97-69.39 in short), in the southwest outskirts of the Large Magellanic Cloud. We present Gemini Flamingos 2 and GSAOI near-infrared imaging of a 3'x3' region around H72.97-69.39 in order to characterize the stellar content of the cluster. The stellar content is probed down to 1.5M{sun}. We find substantial dust extinction across the cluster region, extending up to A_K_ of 3. Deeply embedded stars are associated with ALMA-detected molecular gas suggesting that star formation is ongoing. The high spatial resolution of the GSAOI data allows identification of the central massive object associated with the ^13^CO ALMA observations and detection of fainter low-mass stars around the H30{alpha} ALMA source. The morphology of the molecular gas and the nebulosity from adjacent star formation suggest they have interacted covering a region of several parsecs. The total stellar content in the cluster is estimated from the intermediate and high-mass stellar content to be at least 10000M{sun}, less than R136 with up to 100000M{sun} within 4.7pc radius, but places it in the regime of an SSC. Based on the extinction determination of individual stars we estimate a molecular gas mass in the vicinity of H72.97-69.39 of 6600M{sun}, suggesting more star formation can be expected.
- ID:
- ivo://CDS.VizieR/J/MNRAS/403/1491
- Title:
- Integrated magnitudes of synthetic star clusters
- Short Name:
- J/MNRAS/403/1491
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents integrated magnitudes and colours for synthetic clusters. The integrated parameters have been obtained for the whole cluster population as well as for the main-sequence (MS) population of star clusters. We have also estimated observed integrated magnitudes and colours of the MS population of galactic open clusters, Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) star clusters.
- ID:
- ivo://CDS.VizieR/J/A+A/565/A49
- Title:
- Integrated spectroscopy of 6 LMC clusters
- Short Name:
- J/A+A/565/A49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To increase the number of studied star clusters (SCs) of the Large Magellanic Cloud (LMC), we present flux-calibrated integrated spectra in the optical range ({lambda}=3700-6800{AA}) for six poorly studied LMC SCs of IVA type. This type corresponds to the age range between 200 and 400Myr. We also aim at creating a new template spectrum representative of this age range at the metallicity level of the LMC. Foreground reddening E(B-V) values and ages are derived by applying the template matching method that consists of comparing the line strengths and continuum distribution of the cluster spectra with those of template cluster spectra with known properties. The equivalent width (EW) of the Balmer lines and the diagnostic diagrams involving the sum of EWs of selected spectral lines were also employed as age indicators. For the first time we provide estimates of the clusters' reddenings and ages. As expected, all the clusters appear to be of nearly the same age, their mean value being (400+/-100)Myr, while the resulting mean E(B-V) values range between 0.00 and 0.10mag. The present cluster sample complements previous ones in an effort to gather a spectral library with several clusters per age bin. By averaging the reddening-corrected integrated spectra, weighted by their signal-to-noise (S/N) ratios, a new high S/N ratio template spectrum of 400Myr has been created.
- ID:
- ivo://CDS.VizieR/J/A+A/451/431
- Title:
- IRAS fluxes in LMC starburst regions
- Short Name:
- J/A+A/451/431
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Filamentary structures of early type stars are found to be a common feature of the Magellanic Clouds formed at an age of about 0.9-2x10^8^yr. As we go to younger ages these large structures appear fragmented and sooner or later form young clusters and associations. In the optical domain we have detected 56 such large structures of young objects, known as stellar complexes in the LMC for which we give coordinates and dimensions. We also investigate star formation activity and evolution of these stellar complexes and define the term "starburst region".
- ID:
- ivo://CDS.VizieR/J/ApJ/834/185
- Title:
- IR-bright MSX sources in the SMC with Spitzer/IRS
- Short Name:
- J/ApJ/834/185
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used the Infrared Spectrograph (IRS) on the Spitzer Space Telescope to observe stars in the Small Magellanic Cloud (SMC) selected from the Point Source Catalog of the Midcourse Space Experiment (MSX). We concentrate on the dust properties of the oxygen-rich evolved stars. The dust composition has smaller contributions from alumina compared to the Galaxy. This difference may arise from the lower metallicity in the SMC, but it could be a selection effect, as the SMC sample includes more stars that are brighter and thus more massive. The distribution of the SMC stars along the silicate sequence looks more like the Galactic sample of red supergiants than asymptotic giant branch stars (AGBs). While many of the SMC stars are definitively on the AGB, several also show evidence of hot bottom burning. Three of the supergiants show PAH emission at 11.3{mu}m. Two other sources show mixed chemistry, with both carbon-rich and oxygen-rich spectral features. One, MSX SMC 134, may be the first confirmed silicate/carbon star in the SMC. The other, MSX SMC 049, is a candidate post-AGB star. MSX SMC 145, previously considered a candidate OH/IR star, is actually an AGB star with a background galaxy at z=0.16 along the same line of sight. We consider the overall characteristics of all the MSX sources, the most infrared-bright objects in the SMC, in light of the higher sensitivity and resolution of Spitzer, and compare them with the object types expected from the original selection criteria. This population represents what will be seen in more distant galaxies by the upcoming James Webb Space Telescope (JWST). Color-color diagrams generated from the IRS spectra and the mid-infrared filters on JWST show how one can separate evolved stars from young stellar objects (YSOs) and distinguish among different classes of YSOs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/386/313
- Title:
- IR observations of Mira variables
- Short Name:
- J/MNRAS/386/313
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Published data for large-amplitude asymptotic giant branch variables in the Large Magellanic Cloud (LMC) are re-analysed to establish the constants for an infrared (K) period-luminosity relation of the form MK={rho}[logP-2.38]+{delta}. A slope of {rho}=-3.51+/-0.20 and a zero-point of {delta}=-7.15+/-0.06 are found for oxygen-rich Miras (if a distance modulus of 18.39+/-0.05 is used for the LMC). Assuming this slope is applicable to Galactic Miras we discuss the zero-point for these stars using the revised Hipparcos parallaxes together with published very long baseline interferometry (VLBI) parallaxes for OH masers and Miras in globular clusters. These result in a mean zero-point of {delta}=-7.25+/-0.07 for O-rich Galactic Miras. The zero-point for Miras in the Galactic bulge is not significantly different from this value.
- ID:
- ivo://CDS.VizieR/J/AJ/99/784
- Title:
- IR photometry of LMC long-period variables
- Short Name:
- J/AJ/99/784
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Infrared JHK photometry and visual spectra have been obtained for a large sample of long-period variables (LPVs) in the Large Magellanic Cloud (LMC). Various aspects of the asymptotic giant branch (AGB) evolution of LPVs are discussed using these data. The birth/death rate of LPVs of different ages in the LMC is compared with the birth rates of appropriate samples of planetary nebulae clump stars, Cepheids, and OH/IR stars. It appears that there are much fewer large-amplitude LPVs per unit galactic stellar mass in the LMC than in the Galaxy. We suggest that this may be due to the fact that the evolved intermediate-age AGB stars in the LMC often turn into carbon stars, which tend to have smaller pulsation amplitudes than M stars. There is also a major discrepancy between the number of LPVs in the LMC (and in the Galaxy) and the number predicted by the theories of AGB evolution, pulsation, and mass loss. A distance modulus to the LMC of 18.66+0.05 is derived by comparing the LMC LPVs with P~200days with the 47 Tucanae Mira variables in the (K, logP) plane. The (K, logP) relation is also used to examine the tilt of the LMC populations of old and intermediate-age stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/440/631
- Title:
- IR photometry of LMC O-rich evolved stars
- Short Name:
- J/MNRAS/440/631
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In order to determine the composition of the dust in the circumstellar envelopes of oxygen-rich asymptotic giant branch (AGB) stars, we have computed a grid of MODUST radiative-transfer models for a range of dust compositions, mass-loss rates, dust-shell inner radii and stellar parameters. We compare the resulting colours with the observed oxygen-rich AGB stars from the SAGE-Spec Large Magellanic Cloud (LMC) sample, finding good overall agreement for stars with a mid-infrared excess. We use these models to fit a sample of 37 O-rich AGB stars in the LMC with optically thin circumstellar envelopes, for which 5-35{mu}m Spitzer infrared spectrograph (IRS) spectra and broad-band photometry from the optical to the mid-infrared are available. From the modelling, we find mass-loss rates in the range ~8x10^-8^-5x10^-6^M_{sun}_/yr, and we show that a grain mixture consisting primarily of amorphous silicates, with contributions from amorphous alumina and metallic iron, provides a good fit to the observed spectra. Furthermore, we show from dust models that the AKARI [11]-[15] versus [3.2]-[7] colour-colour diagram is able to determine the fractional abundance of alumina in O-rich AGB stars.
- 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.
