- ID:
- ivo://CDS.VizieR/J/A+A/347/841
- Title:
- HST Observations of SMC N88A
- Short Name:
- J/A+A/347/841
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High-resolution Hubble Space Telescope images have allowed us for the first time to resolve the compact SMC ionized ``blob'' N88A (diameter ~3.5arcsec or 1pc). This very young HII, region, which is hatching from its natal molecular cloud, is heavily affected by absorbing dust associated with the cloud. The interstellar reddening towards N88A is on average A_v_~1.5mag and strikingly rises to more than 3.5mag in a narrow dust band crossing the core of the HII region. Such a high extinction is unprecedented for an HII region in the metal-poor SMC. We present the photometry of some 70 stars lying towards the OB association at the center of which lies N88A. The exciting star(s) of N88A is not detected, due to the heavy extinction. The chronology of star formation is discussed for the whole region.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/886/99
- Title:
- HST obs. in the region of 3 young LMC SNIa remnants
- Short Name:
- J/ApJ/886/99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used two methods to search for surviving companions of Type Ia supernova progenitors in three Balmer-dominated supernova remnants in the Large Magellanic Cloud: 0519-69.0, 0505-67.9 (DEM L71), and 0548-70.4. In the first method, we use the Hubble Space Telescope photometric measurements of stars to construct color-magnitude diagrams (CMDs) and compare positions of stars in the CMDs with those expected from theoretical post-impact evolution of surviving main-sequence or helium star companions. No obvious candidates of surviving companions are identified in this photometric search. Future models for surviving red giant companions or with different explosion mechanisms are needed for thorough comparisons with these observations in order to make more definitive conclusions. In the second method, we use Multi Unit Spectroscopic Explorer observations of 0519-69.0 and DEM L71 to carry out spectroscopic analyses of stars in order to use large peculiar radial velocities as diagnostics of surviving companions. We find a star in 0519-69.0 and a star in DEM L71 moving at radial velocities of 182+/-0km/s and 213+/-0km/s, respectively, more than 2.5{sigma} from the mean radial velocity of the underlying stellar population, 264 and 270km/s, respectively. These stars need higher-quality spectra to investigate their abundances and rotation velocities to determine whether they are indeed surviving companions of the supernova progenitors.
- ID:
- ivo://CDS.VizieR/J/ApJ/672/914
- Title:
- HST photometry in NGC 346
- Short Name:
- J/ApJ/672/914
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the third part of our photometric study of the star-forming region NGC 346/N66 and its surrounding field in the Small Magellanic Cloud (SMC), we focus on the large number of low-mass pre-main-sequence (PMS) stars revealed by the Hubble Space Telescope observations with the Advanced Camera for Surveys. We investigate the origin of the observed broadening of the PMS population in the V-I,V color-magnitude diagram. The most likely explanations are either the presence of differential reddening or an age spread among the young stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/448/179
- Title:
- HST photometry in R136
- Short Name:
- J/ApJ/448/179
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have analyzed Hubble Space Telescope (HST) images of the compact, luminous star cluster R136 in the LMC that were taken with the refurbished HST and new Wide Field/Planetary Camera. These images allow us to examine the stellar population in a region of unusually intense star formation at a scale of 0.01pc. We have detected stars to 23.5 in F555W and have quantified the stellar population to an M_555.0 of 0.9 or a mass of 2.8M_{sun}_. Comparisons of HR diagrams with isochrones that were constructed for the HST flight filter system from theoretical stellar evolutionary tracks reveal massive stars, a main sequence to at least 2.8M_{sun}_, and stars with M_555.0>=0.5 still on pre-main sequence tracks. The average stellar population is fit with a 3-4Myr isochrone. Contrary to expectations from star formation models, however, the formation period for the massive stars and lower mass stars appear to largely overlap. We have measured the IMF for stars 2.8-15M_{sun}_ in three annuli from 0.5-4.7pc from the center of the cluster. The slopes of the IMF in all three annuli are the same within the uncertainties, thus, showing no evidence for mass segregation beyond 0.5pc. Furthermore, the combined IMF slope, -1.22+/-0.06, is close to a normal Salpeter IMF. The lower mass limit must be lower than the limits of our measurements: <=2.8M_{sun}_ beyond 0.5pc and <=7M_{sun}_ within 0.1pc. This is contrary to some predictions that the lower mass limit could be as high as 10M_{sun}_ in regions of intense massive star formation. Integrated properties of R136 are consistent with its being comparable to a rather small globular cluster when such clusters were the same age as R136. From the surface brightness profile, an upper limit for core radius of 0.02pc is set. Within a radius of 0.4pc we estimate that there have been roughly 20 crossing times and relaxation should be well along. Within 0.5pc crowding prevents us from detecting the intermediate mass population, but there is a hint of an excess of stars brighter than M_555.0=-5 and of a deficit in the highest mass stars between 0.6pc and 1.2pc. This would be consistent with dynamical segregation.
- ID:
- ivo://CDS.VizieR/J/AJ/130/1083
- Title:
- HST photometry in the wing of the SMC
- Short Name:
- J/AJ/130/1083
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used the Wide Field Planetary Camera 2 (WFPC2) on the Hubble Space Telescope to image a star field in the wing of the Small Magellanic Cloud (SMC), near the HII region N81. The images were taken in the F336W, F547M, F675W, and F814W filters. From photometry of stars in this field, we construct color-magnitude diagrams (CMDs) for about 4200 stars and compare them with theoretical isochrones.
- ID:
- ivo://CDS.VizieR/J/A+A/381/941
- Title:
- HST photometry of stars in N160A
- Short Name:
- J/A+A/381/941
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using high-resolution imaging with the Hubble Space Telescope, we study the Large Magellanic Cloud 2 region N160A and uncover several striking features of this complex massive star-forming site. The two compact high excitation 2 blobs (HEBs) A1 and A2 are for the first time resolved and their stellar content and morphology is revealed. A1, being of higher excitation, is powered by a single massive star whose strong wind has created a surrounding bubble. A2 harbors several exciting stars enshrouded by large quantities of dust. The whole N160A nebula is energized by three star clusters for which we obtain photometry and study their color-magnitude diagram. The 2 region is particularly dusty, with extinction values reaching an A_V_~2.5mag in the visible, and it is separated from the molecular cloud by an outstanding ionization front. A previously detected infrared young stellar object is also accurately located with respect to the 2 region (N160A).
- ID:
- ivo://CDS.VizieR/J/ApJ/707/1417
- Title:
- HST view of YSOs in the LMC
- Short Name:
- J/ApJ/707/1417
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used archival Hubble Space Telecope (HST) H{alpha} images to study the immediate environments of massive and intermediate-mass young stellar object (YSO) candidates in the Large Magellanic Cloud (LMC). The sample of YSO candidates, taken from Gruendl & Chu (2009, Cat. J/ApJS/184/172), was selected based on Spitzer IRAC and MIPS observations of the entire LMC and complementary ground-based optical and near-infrared observations. We found HST H{alpha} images for 99 YSO candidates in the LMC, of which 82 appear to be genuine YSOs. More than 95% of the YSOs are found to be associated with molecular clouds. YSOs are seen in three different kinds of environments in the H{alpha} images: in dark clouds, inside or on the tip of bright-rimmed dust pillars, and in small HII regions. Comparisons of spectral energy distributions for YSOs in these three different kinds of environments suggest that YSOs in dark clouds are the youngest, YSOs with small HII regions are the most evolved, and YSOs in bright-rimmed dust pillars span a range of intermediate evolutionary stages. This rough evolutionary sequence is substantiated by the presence of silicate absorption features in the Spitzer Infrared Spectrograph spectra of some YSOs in dark clouds and in bright-rimmed dust pillars, but not those of YSOs in small HII regions. We present a discussion on triggered star formation for YSOs in bright-rimmed dust pillars or in dark clouds adjacent to HII regions. As many as 50% of the YSOs are resolved into multiple sources in high-resolution HST images.
- ID:
- ivo://CDS.VizieR/J/MNRAS/300/665
- Title:
- HST VI Photometry of Six LMC Old Globular Clusters
- Short Name:
- J/MNRAS/300/665
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The following tables contain the results of photometry performed on Hubble Space Telescope WFPC2 images of the Large Magellanic Cloud globular clusters NGC 1754, 1835, 1898, 1916, 2005, and 2019. The magnitudes reported here were measured from Planetary Camera F555W and F814W images using DoPHOT (Schechter, Mateo, & Saha 1993) and afterwards transformed to Johnson V/Kron-Cousins I using equation 9 of Holtzman et al. (1995PASP..107.1065H). We carried out photometry on both long (1500 sec combined in F555W, 1800 sec in F814W) and short (40 sec combined in F555W, 60 sec in F814W) exposures. Where the short exposure photometry produced smaller errors, we report those magnitudes in place of those measured from the long exposures. For each star, we give an integer identifier, its x and y pixel position as measured in the F555W PC image, its V and I magnitude, the photometric errors reported by DoPHOT, both the V and I DoPHOT object types (multiplied by 10 if the reported magnitude was measured in the short exposure frame), and a flag if the star was removed during our procedure for statistical field star subtraction. Summary of data reduction and assessment of photometric accuracy: Cosmic ray rejection, correction for the y-dependent CTE effect (Holtzman et al. 1995a), geometric distortion correction, and bad pixel flagging were applied to the images before performing photometry. For the photometry, we used version 2.5 of DoPHOT, modified by Eric Deutsch to handle floating-point images. We found that there were insufficient numbers of bright, isolated stars in the PC frames for producing aperture corrections. Aperture corrections as a function of position in the frame were instead derived using WFPC2 point spread functions kindly provided by Peter Stetson. As these artificially generated aperture corrections agree well with ones derived from isolated stars in the WF chips, we trust that they are reliable to better than 0.05 mag. In agreement with the report of Whitmore & Heyer (1997), we found an offset in mean magnitudes between the short- and long-exposure photometry. We corrected for this effect by adjusting the short-exposure magnitudes to match, on average, those of the long exposures. Finally, we merged the short- and long- exposure lists of photometry as described above and transformed the magnitudes from the WFPC2 system to Johnson V/Kron-Cousins I, applying the Holtzman et al. (1995PASP..107.1065H) zero points. Statistical field star subtraction was performed using color-magnitude diagrams of the field stars produced from the combined WF frames. Completeness and random and systematic errors in the photometry were extensively modelled through artificial star tests. Crowding causes the completeness to be a strong function of position in the frame, with detection being most difficult near the cluster centers. In addition, we found that crowding introduces systematic errors in the photometry, generally <0.05 mag, that depend on the V-I and V of the star. Fortunately, these errors are well-understood. However, unknown errors in the zero points may persist at the ~0.05 mag level.
- ID:
- ivo://CDS.VizieR/J/ApJ/738/137
- Title:
- HST VI stars in Shapley Constellation III
- Short Name:
- J/ApJ/738/137
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present our investigation of pre-main-sequence (PMS) stellar populations in the Large Magellanic Cloud (LMC) from imaging with Hubble Space Telescope Wide-Field Planetary Camera 2. Our targets of interest are four star-forming regions located at the periphery of the super-giant shell LMC 4 (Shapley Constellation III). The PMS stellar content of the regions is revealed through the differential Hess diagrams and the observed color-magnitude diagrams (CMDs). Further statistical analysis of stellar distributions along cross sections of the faint part of the CMDs allowed the quantitative assessment of the PMS stars census, and the isolation of faint PMS stars as the true low-mass stellar members of the regions. These distributions are found to be well represented by a double-Gaussian function, the first component of which represents the main-sequence field stars and the second the native PMS stars of each region. Based on this result, a cluster membership probability was assigned to each PMS star according to its CMD position. The higher extinction in the region LH 88 did not allow the unambiguous identification of its native stellar population. The CMD distributions of the PMS stars with the highest membership probability in the regions LH 60, LH 63, and LH 72 exhibit an extraordinary similarity among the regions, suggesting that these stars share common characteristics, as well as common recent star formation history. Considering that the regions are located at different areas of the edge of LMC 4, this finding suggests that star formation along the super-giant shell may have occurred almost simultaneously.
- ID:
- ivo://CDS.VizieR/J/AJ/152/164
- Title:
- I-band light curves of OGLE LMC Miras
- Short Name:
- J/AJ/152/164
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We develop a nonlinear semi-parametric Gaussian process model to estimate periods of Miras with sparsely sampled light curves. The model uses a sinusoidal basis for the periodic variation and a Gaussian process for the stochastic changes. We use maximum likelihood to estimate the period and the parameters of the Gaussian process, while integrating out the effects of other nuisance parameters in the model with respect to a suitable prior distribution obtained from earlier studies. Since the likelihood is highly multimodal for period, we implement a hybrid method that applies the quasi-Newton algorithm for Gaussian process parameters and search the period/frequency parameter space over a dense grid. A large-scale, high-fidelity simulation is conducted to mimic the sampling quality of Mira light curves obtained by the M33 Synoptic Stellar Survey. The simulated data set is publicly available and can serve as a testbed for future evaluation of different period estimation methods. The semi-parametric model outperforms an existing algorithm on this simulated test data set as measured by period recovery rate and quality of the resulting period-luminosity relations.
