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- ID:
- ivo://CDS.VizieR/J/A+A/656/A66
- Title:
- Semi-regular red giants as distance indicators
- Short Name:
- J/A+A/656/A66
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Semi-regular variables (SRVs) are similar to Miras in brightness, and they also follow PLRs, though not necessarily the same as Miras. As potential standard candles they are more challenging than Miras due to their smaller variability amplitudes and less regular light curves, but they are substantially more numerous and especially promising to probe old stellar populations. We aim to characterize the variability of SRVs, with focus on their connection with Miras, in order to prepare the ground for investigating their potential as distance indicators. We examine SRVs and Miras in the Magellanic Clouds from OGLE-III observations, with data from Gaia and 2MASS. After cleaning the sample from variability periods unrelated to pulsation, we classify each source by chemical type and combination of pulsation modes. We examine the results in terms of global photometric and pulsation properties. We identify four SRVs groups that fit the general evolutionary scenario predicted by theory. SRVs dominated by fundamental-mode pulsation are very similar to Miras, especially if mono-periodic. They further split into two sub-groups, one of which follows the same sequence as Miras in the period-luminosity and period-amplitude diagram, without discontinuity. The similarities between Miras and SRVs suggest that the latter can be adopted as complementary distance indicators to the former, thereby at least doubling the available number of LPVs suitable for use as distance indicators. The traditional amplitude-based separation between Miras and SRVs is not necessarily appropriate, and a more physically sound criterion should also involve pulsation periods. While this would require comparatively longer time series, they are expected to become accessible in the coming years even for weak sources thanks to current and future large-scale surveys. The table of reclassified LPVs is made public.
- ID:
- ivo://CDS.VizieR/J/A+A/471/103
- Title:
- SIMBA observations of SMC
- Short Name:
- J/A+A/471/103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- CO observations have been the best way so far to trace molecular gas in external galaxies, but in low metallicity environments the gas mass deduced could be largely underestimated due to enhanced photodissociation of the CO molecule. Large envelopes of H_2_ could therefore be missed by CO observations. At present, the kinematic information of CO data cubes are used to estimate virial masses and trace the total mass of the molecular clouds. Millimeter dust emission can also be used as a dense gas tracer and could unveil H_2_ envelopes lacking CO. These different tracers must be compared in different environments. This study compares virial masses to masses deduced from millimeter emission, in two GMC samples: the local molecular clouds in our Galaxy (10^4^-10^5^M_{sun}_), and their equivalents in the Small Magellanic Cloud (SMC), one of the nearest low metallicity dwarf galaxies. In our Galaxy, mass estimates deduced from millimeter (FIRAS) emission are consistent with masses deduced from gamma ray analysis and therefore trace the total mass of the clouds. Virial masses are systematically larger (twice on average) than mass estimates from millimeter dust emission. This difference decreases toward high masses and has been reported in previous studies. This is not the case for SMC giant molecular clouds: molecular cloud masses deduced from SIMBA millimeter observations are systematically higher (twice on average for conservative values of the dust to gas ratio and dust emissivity) than the virial masses from SEST CO observations. The observed excess cannot be accounted for by any plausible change of dust properties. Taking a general form for the virial theorem, we show that a magnetic field strength of ~15{mu}G in SMC clouds could provide additional support for the clouds and explain the difference observed. We conclude that masses of SMC molecular clouds have so far been underestimated. Magnetic pressure may contribute significantly to their support.
- ID:
- ivo://CDS.VizieR/J/MNRAS/478/1425
- Title:
- Single-mode OGLE Cepheids additional modes
- Short Name:
- J/MNRAS/478/1425
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Detailed knowledge of the variability of classical Cepheids, in particular their modulations and mode composition, provides crucial insight into stellar structure and pulsation. However, tiny modulations of the dominant radial-mode pulsation were recently found to be very frequent, possibly ubiquitous in Cepheids, which makes secondary modes difficult to detect and analyse, since these modulations can easily mask the potentially weak secondary modes. The aim of this study is to re-investigate the secondary mode content in the sample of OGLE-III and OGLE-IV single-mode classical Cepheids using kernel regression with adaptive kernel width for pre-whitening, instead of using a constant-parameter model. This leads to a more precise removal of the modulated dominant pulsation, and enables a more complete survey of secondary modes with frequencies outside a narrow range around the primary. Our analysis reveals that significant secondary modes occur more frequently among first overtone Cepheids than previously thought. The mode composition appears significantly different in the Large and Small Magellanic Clouds, suggesting a possible dependence on chemical composition. In addition to the formerly identified non-radial mode at P_2_~=0.6...0.65P_1_ (0.62-mode), and a cluster of modes with near-primary frequency, we find two more candidate non-radial modes. One is a numerous group of secondary modes with P_2_~=1.25P_1_, which may represent the fundamental of the 0.62-mode, supposed to be the first harmonic of an l {in} {7, 8, 9} non-radial mode. The other new mode is at P_2_ ~=1.46P_1_, possibly analogous to a similar, rare mode recently discovered among first overtone RR Lyrae stars.
- ID:
- ivo://CDS.VizieR/J/A+A/600/A16
- Title:
- Six LMC star forming region spectra
- Short Name:
- J/A+A/600/A16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The kinetic temperature of molecular clouds is a fundamental physical parameter affecting star formation and the initial mass function. The Large Magellanic Cloud (LMC), the closest star forming galaxy with low metallicity, provides an ideal laboratory to study star formation in such an environment. The classical dense molecular gas thermometer NH_3_ is rarely available in a low metallicity environment because of photoionization and a lack of nitrogen atoms. Our goal is to directly measure the gas kinetic temperature with formaldehyde toward six star-forming regions in the LMC. Three rotational transitions (J_KAKC_ = 3_03_-2_02_, 3_22_-2_21_, and 3_21_-2_20_) of para-H_2_CO near 218GHz were observed with the Atacama Pathfinder EXperiment (APEX) 12m telescope toward six star forming regions in the LMC. Those data are complemented by C^18^O 2-1 spectra.
- ID:
- ivo://CDS.VizieR/J/AJ/161/74
- Title:
- SMASH DR2. 197 SMASH fields
- Short Name:
- J/AJ/161/74
- Date:
- 19 Jan 2022 09:37:25
- Publisher:
- CDS
- Description:
- The Large and Small Magellanic Clouds (LMC and SMC) are the largest satellite galaxies of the Milky Way and close enough to allow for a detailed exploration of their structure and formation history. The Survey of the MAgellanic Stellar History (SMASH) is a community Dark Energy Camera (DECam) survey of the Magellanic Clouds using ~50 nights to sample over ~2400deg^2^ centered on the Clouds at ~20% filling factor (but with contiguous coverage in the central regions) and to depths of ~24th mag in ugriz. The primary goals of SMASH are to map out the extended stellar peripheries of the Clouds and uncover their complicated interaction and accretion history as well as to derive spatially resolved star formation histories of the central regions and create a "movie" of their past star formation. Here we announce the second SMASH public data release (DR2), which contains all 197 fully calibrated DECam fields including the main body fields in the central regions. The DR2 data are available through the Astro Data Lab hosted by the NSF's National Optical-Infrared Astronomy Research Laboratory. We highlight three science cases that make use of the SMASH DR2 data and will be published in the future: (1) preliminary star formation histories of the LMC, (2) the search for Magellanic star clusters using citizen scientists, and, (3) photometric metallicities of Magellanic Cloud stars using the DECam u-band.
- ID:
- ivo://CDS.VizieR/J/AJ/154/199
- Title:
- SMASH: Survey of the MAgellanic Stellar History
- Short Name:
- J/AJ/154/199
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Large and Small Magellanic Clouds are unique local laboratories for studying the formation and evolution of small galaxies in exquisite detail. The Survey of the MAgellanic Stellar History (SMASH) is an NOAO community Dark Energy Camera (DECam) survey of the Clouds mapping 480 deg^2^ (distributed over ~2400 square degrees at ~20% filling factor) to ~24th mag in ugriz. The primary goals of SMASH are to identify low surface brightness stellar populations associated with the stellar halos and tidal debris of the Clouds, and to derive spatially resolved star formation histories. Here, we present a summary of the survey, its data reduction, and a description of the first public Data Release (DR1). The SMASH DECam data have been reduced with a combination of the NOAO Community Pipeline, the PHOTRED automated point-spread-function photometry pipeline, and custom calibration software. The astrometric precision is ~15 mas and the accuracy is ~2 mas with respect to the Gaia reference frame. The photometric precision is ~0.5%-0.7% in griz and ~1% in u with a calibration accuracy of ~1.3% in all bands. The median 5{sigma} point source depths in ugriz are 23.9, 24.8, 24.5, 24.2, and 23.5 mag. The SMASH data have already been used to discover the Hydra II Milky Way satellite, the SMASH 1 old globular cluster likely associated with the LMC, and extended stellar populations around the LMC out to R~18.4 kpc. SMASH DR1 contains measurements of ~100 million objects distributed in 61 fields. A prototype version of the NOAO Data Lab provides data access and exploration tools.
- ID:
- ivo://CDS.VizieR/J/A+A/622/A29
- Title:
- SMC AGN in XMM-Newton
- Short Name:
- J/A+A/622/A29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Finding active galactic nuclei (AGN) behind the Magellanic Clouds (MCs) is difficult because of the high stellar density in these fields. Although the first AGN behind the Small Magellanic Cloud (SMC) were reported in the 1980s, it is only recently that the number of AGN known behind the SMC has increased by several orders of magnitude. The mid-infrared colour selection technique has proven to be an efficient means of identifying AGN, especially obscured sources. The X-ray regime is complementary in this regard and we use XMM-Newton observations to support the identification of AGN behind the SMC. We present a catalogue of AGN behind the SMC by correlating an updated X-ray point-source catalogue from our XMM-Newton survey of the SMC with previously identified AGN from the literature as well as a list of candidates obtained from the ALLWISE mid-infrared colour-selection criterion. We studied the properties of the sample with respect to their redshifts, luminosities, and X-ray spectral characteristics. We also identified the near-infrared counterpart of the sources from the VISTA observations. The redshift and luminosity distributions of the sample (where known) indicate that we detect sources ranging from nearby Seyfert galaxies to distant and obscured quasars. The X-ray hardness ratios are compatible with those typically expected for AGN, and the VISTA colours and variability are also consistent with AGN. A positive correlation was observed between the integrated X-ray flux (0.2-12keV) and the ALLWISE and VISTA magnitudes. We further present a sample of new candidate AGN and candidates for obscured AGN. Together these make an interesting subset for further follow-up studies. An initial spectroscopic follow-up of 6 out of the 81 new candidates showed that all six sources are active galaxies, although two have narrow emission lines.
- ID:
- ivo://CDS.VizieR/J/ApJS/101/41
- Title:
- SMC and Bridge extended catalog
- Short Name:
- J/ApJS/101/41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A survey of extended objects in the Magellanic System was carried out on the ESO/SERC R and J Sky Survey Atlases. The present work is dedicated to the Small Magellanic Cloud and to the inter-Magellanic Cloud region ("Bridge") totaling 1188 objects, of which 554 are classified as star clusters, 343 are emissionless associations, and 291 are related to emission nebulae. The survey includes cross-identifications among catalogs, and we present 284 new objects. We provide accurate positions, classification, homogeneous sizes, and position angles, as well as information on cluster pairs and hierarchical relation for superimposed objects. Two clumps of extended objects in the Bridge and one at the Small Magellanic Cloud wing tip might be currently forming dwarf spheroidal galaxies.
- ID:
- ivo://CDS.VizieR/J/A+A/393/887
- Title:
- SMC Be stars candidates
- Short Name:
- J/A+A/393/887
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recently the OGLE experiment has provided accurate light curves and colours for about 2 millions stars in the Small Magellanic Cloud. We have examined this database for its content of Be stars, applying some selection criteria, and we have found a sample of ~1000 candidates. Some of these stars show beautiful light curves with amazing variations never observed in any Galactic variable. We find outbursts in 13% of the sample (type-1 stars), high and low states in 15%, periodic variations in 7%, and the usual variations seen in Galactic Be stars in 65% of the cases. The Galactic counterparts of type-1 objects could be the outbursting Be stars found by Hubert & Floquet (1998, Cat. J/A+A/335/565) after the analysis of Hipparcos photometry. We discuss the possibility that type-1 stars could correspond to Be stars with accreting white dwarf companions or alternatively, blue pre-main sequence stars surrounded by thermally unstable accretion disks. We provide coordinates and basic photometric information for these stars and some examples of light curves.
