- ID:
- ivo://CDS.VizieR/J/ApJ/857/132
- Title:
- gri photometry of NGC 796 cluster
- Short Name:
- J/ApJ/857/132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 796 is a massive young cluster located 59kpc from us in the diffuse intergalactic medium of the 1/5-1/10Z_{sun}_ Magellanic Bridge, allowing us to probe variations in star formation and stellar evolution processes as a function of metallicity in a resolved fashion, and providing a link between resolved studies of nearby solar-metallicity and unresolved distant metal-poor clusters located in high-redshift galaxies. In this paper, we present adaptive optics griH{alpha} imaging of NGC 796 (at 0.5", which is ~0.14pc at the cluster distance) along with optical spectroscopy of two bright members to quantify the cluster properties. Our aim is to explore whether star formation and stellar evolution vary as a function of metallicity by comparing the properties of NGC 796 to higher-metallicity clusters. We find an age of 20_-5_^+12^Myr from isochronal fitting of the cluster main sequence in the color-magnitude diagram. Based on the cluster luminosity function, we derive a top-heavy stellar initial mass function (IMF) with a slope {alpha}=1.99+/-0.2, hinting at a metallicity and/or environmental dependence of the IMF, which may lead to a top-heavy IMF in the early universe. Study of the H{alpha} emission-line stars reveals that classical Be stars constitute a higher fraction of the total B-type stars when compared with similar clusters at greater metallicity, providing some support to the chemically homogeneous theory of stellar evolution. Overall, NGC 796 has a total estimated mass of 990+/-200M_{sun}_, and a core radius of 1.4+/-0.3pc, which classifies it as a massive young open cluster, unique in the diffuse interstellar medium of the Magellanic Bridge.
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- ID:
- ivo://CDS.VizieR/J/A+A/509/A11
- Title:
- H{alpha} emission-line objects in SMC clusters
- Short Name:
- J/A+A/509/A11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Slitless CCD spectra were obtained covering the bulk (about 3 square degrees) of the Small Magellanic Cloud. For H{alpha} line-emission twice as strong as the ambient continuum, the survey is complete to spectral type B2/B3 on the main sequence. About 8120 spectra of 4437 stars were searched for emission lines in 84 open clusters, and 370 emission-line stars were found, among them at least 231 close to the main sequence. For 176 of them, photometry is available from the OGLE database. For comparison with a higher-metallicity environment, the Galactic sample of the photometric H{alpha} survey by McSwain & Gies (2005, Cat. <J/ApJS/161/118>) was used. Among early spectral sub-types, Be stars are more frequent by a factor ~3-5 in the SMC than in the Galaxy. The distribution with spectral type is similar in both galaxies, i.e., not strongly dependent on metallicity. The fraction of Be stars does not seem to vary with local star density. The Be phenomenon mainly sets in towards the end of the main-sequence evolution (this trend may be more pronounced in the SMC); but some Be stars already form with Be-star characteristics. In small subsamples (such as single clusters), even if they appear identical, the fraction of emission-line stars can deviate drastically from the mean. In all probability, the fractional critical angular rotation rate, OMC, is one of the main parameters governing the occurrence of the Be phenomenon. If the Be character is only acquired during the course of evolution, the key circumstance is the evolution of OMC, which is not only dependent on metallicity but differently so for different mass ranges. As a result, even if the Be phenomenon is driven basically by a single parameter (namely OMC), it can assume a complex multi-parametric appearance. The large cluster-to-cluster differences, which seem stronger than all other variations, serve as a caveat that this big picture may undergo significant second-order modulations (e.g., pulsations, initial angular momentum, etc).
- ID:
- ivo://CDS.VizieR/J/AJ/158/192
- Title:
- He II emission from Wolf-Rayet stars in MW & LMC
- Short Name:
- J/AJ/158/192
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We calibrated a technique to measure dust attenuation in star-forming galaxies. The technique utilizes the stellar-wind lines in Wolf-Rayet stars, which are widely observed in galaxy spectra. The He II 1640 and 4686 features are recombination lines whose ratio is largely determined by atomic physics. Therefore they can serve as a stellar dust probe in the same way as the Balmer lines are used as a nebular probe. We measured the strength of the He II 1640 line in 97 Wolf-Rayet stars in the Galaxy and the Large Magellanic Cloud. The reddening corrected fluxes follow a tight correlation with a fixed ratio of 7.76 for the He II 1640 to 4686 line ratio. Dust attenuation decreases this ratio. We provide a relation between the stellar E(B-V) and the observed line ratio for several attenuation laws. Combining this technique with the use of the nebular Balmer decrement allows the determination of the stellar and nebular dust attenuation in galaxies and can probe its effects at different stellar age and mass regimes, independently of the initial mass function and the star formation history. We derived the dust reddening from the He II line fluxes and compared it to the reddening from the Balmer decrement and from the slope of the ultraviolet continuum in two star-forming galaxies. The three methods result in dust attenuations which agree to within the errors. Future application of this technique permits studies of the stellar dust attenuation compared to the nebular attenuation in a representative galaxy sample.
- ID:
- ivo://irsa.ipac/Herschel/Catalog/HERITAGE/HERITAGE_LMC_BM
- Title:
- HERITAGE LMC Band-Matched Catalog
- Short Name:
- HERITAGE_LMC_BM
- Date:
- 01 Oct 2018 20:27:20
- Publisher:
- NASA/IPAC Infrared Science Archive
- Description:
- Observations from the HERschel Inventory of the Agents of Galaxy Evolution (HERITAGE) have been used to identify dusty populations of sources in the Large and Small Magellanic Clouds (LMC and SMC). The study used the HERITAGE catalogs of point sources from both the Photodetector Array Camera and Spectrometer (PACS; 100 and 160 microns) and Spectral and Photometric Imaging Receiver (SPIRE; 250, 350, and 500 microns) cameras. These catalogs are matched to each other to create a Herschel band-merged catalog and then further matched to archival Spitzer IRAC and MIPS catalogs from the Spitzer Surveying the Agents of Galaxy Evolution (SAGE) and SAGE-SMC surveys to create single mid- to far-infrared (far-IR) point source catalogs that span the wavelength range from 3.6 to 500 microns. There are 35,322 unique sources in the LMC and 7503 in the SMC.
- ID:
- ivo://irsa.ipac/Herschel/Catalog/HERITAGE/HERITAGELBMClass
- Title:
- HERITAGE LMC Band-Matched Classification Table
- Short Name:
- HERITAGELBMClass
- Date:
- 01 Oct 2018 20:27:20
- Publisher:
- NASA/IPAC Infrared Science Archive
- Description:
- Observations from the HERschel Inventory of the Agents of Galaxy Evolution (HERITAGE) have been used to identify dusty populations of sources in the Large and Small Magellanic Clouds (LMC and SMC). The study used the HERITAGE catalogs of point sources from both the Photodetector Array Camera and Spectrometer (PACS; 100 and 160 microns) and Spectral and Photometric Imaging Receiver (SPIRE; 250, 350, and 500 microns) cameras. These catalogs are matched to each other to create a Herschel band-merged catalog and then further matched to archival Spitzer IRAC and MIPS catalogs from the Spitzer Surveying the Agents of Galaxy Evolution (SAGE) and SAGE-SMC surveys to create single mid- to far-infrared (far-IR) point source catalogs that span the wavelength range from 3.6 to 500 microns. There are 35,322 unique sources in the LMC and 7503 in the SMC. The Band-Matched Classification Tables identify matches to literature catalogs of previously classified LMC and SMC objects.
- ID:
- ivo://irsa.ipac/Herschel/Catalog/HERITAGE/LMC_PACS100
- Title:
- HERITAGE LMC PACS 100 micron Catalog
- Short Name:
- HERITAGE LMC100
- Date:
- 01 Oct 2018 20:27:20
- Publisher:
- NASA/IPAC Infrared Science Archive
- Description:
- The HERschel Inventory of The Agents of Galaxy Evolution (HERITAGE) open time key program mapped the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) at 100, 160, 250, 350, and 500 microns using Herschel's PACS and SPIRE instruments. The overriding science goal of HERITAGE is to study the life cycle of matter as traced by dust in the LMC and SMC.
- ID:
- ivo://irsa.ipac/Herschel/Catalog/HERITAGE/LMC_PACS160
- Title:
- HERITAGE LMC PACS 160 micron Catalog
- Short Name:
- HERITAGE LMC160
- Date:
- 01 Oct 2018 20:27:20
- Publisher:
- NASA/IPAC Infrared Science Archive
- Description:
- The HERschel Inventory of The Agents of Galaxy Evolution (HERITAGE) open time key program mapped the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) at 100, 160, 250, 350, and 500 microns using Herschel's PACS and SPIRE instruments. The overriding science goal of HERITAGE is to study the life cycle of matter as traced by dust in the LMC and SMC.
- ID:
- ivo://irsa.ipac/Herschel/Catalog/HERITAGE/LMC_SPIRE500
- Title:
- HERITAGE LMC SPIRE 500 micron Catalog
- Short Name:
- HERITAGE LMC500
- Date:
- 01 Oct 2018 20:27:20
- Publisher:
- NASA/IPAC Infrared Science Archive
- Description:
- The HERschel Inventory of The Agents of Galaxy Evolution (HERITAGE) open time key program mapped the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) at 100, 160, 250, 350, and 500 microns using Herschel's PACS and SPIRE instruments. The overriding science goal of HERITAGE is to study the life cycle of matter as traced by dust in the LMC and SMC.
- ID:
- ivo://irsa.ipac/Herschel/Catalog/HERITAGE/LMC_SPIRE350
- Title:
- HERITAGE LMC SPIRE 350 micron Catalog
- Short Name:
- HERITAGE LMC350
- Date:
- 01 Oct 2018 20:27:20
- Publisher:
- NASA/IPAC Infrared Science Archive
- Description:
- The HERschel Inventory of The Agents of Galaxy Evolution (HERITAGE) open time key program mapped the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) at 100, 160, 250, 350, and 500 microns using Herschel's PACS and SPIRE instruments. The overriding science goal of HERITAGE is to study the life cycle of matter as traced by dust in the LMC and SMC.
- ID:
- ivo://irsa.ipac/Herschel/Catalog/HERITAGE/LMC_SPIRE250
- Title:
- HERITAGE LMC SPIRE 250 micron Catalog
- Short Name:
- HERITAGE LMC250
- Date:
- 01 Oct 2018 20:27:20
- Publisher:
- NASA/IPAC Infrared Science Archive
- Description:
- The HERschel Inventory of The Agents of Galaxy Evolution (HERITAGE) open time key program mapped the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) at 100, 160, 250, 350, and 500 microns using Herschel's PACS and SPIRE instruments. The overriding science goal of HERITAGE is to study the life cycle of matter as traced by dust in the LMC and SMC.
