- ID:
- ivo://CDS.VizieR/J/ApJ/812/158
- Title:
- Leo P RR Lyrae candidates & cumulative SFH
- Short Name:
- J/ApJ/812/158
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Leo P is a low-luminosity dwarf galaxy discovered through the blind HI Arecibo Legacy Fast ALFA survey. The HI and follow-up optical observations have shown that Leo P is a gas-rich dwarf galaxy with active star formation, an underlying older population, and an extremely low oxygen abundance. We have obtained optical imaging with the Hubble Space Telescope to two magnitudes below the red clump in order to study the evolution of Leo P. We refine the distance measurement to Leo P to be 1.62+/-0.15Mpc, based on the luminosity of the horizontal branch stars and 10 newly identified RR Lyrae candidates. This places the galaxy at the edge of the Local Group, ~0.4Mpc from Sextans B, the nearest galaxy in the NGC 3109 association of dwarf galaxies of which Leo P is clearly a member. The star responsible for ionizing the HII region is most likely an O7V or O8V spectral type, with a stellar mass >~25M_{sun}_. The presence of this star provides observational evidence that massive stars at the upper end of the initial mass function are capable of being formed at star formation rates as low as ~10^-5^M_{sun}_/yr. The best-fitting star formation history (SFH) derived from the resolved stellar populations of Leo P using the latest PARSEC models shows a relatively constant star formation rate over the lifetime of the galaxy. The modeled luminosity characteristics of Leo P at early times are consistent with low-luminosity dSph Milky Way satellites, suggesting that Leo P is what a low-mass dSph would look like if it evolved in isolation and retained its gas. Despite the very low mass of Leo P, the imprint of reionization on its SFHIs subtle at best, and consistent with being totally negligible. The isolation of Leo P, and the total quenching of star formation of Milky Way satellites of similar mass, implies that the local environment dominates the quenching of the Milky Way satellites.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/421/78
- Title:
- LMC pre-main sequences stars mass accretion rates
- Short Name:
- J/MNRAS/421/78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a multiwavelength study of three star-forming regions, spanning the age range 1-14Myr, located between the 30 Doradus complex and supernova SN 1987A in the Large Magellanic Cloud (LMC). We reliably identify about 1000 pre-main-sequence (PMS) star candidates actively undergoing mass accretion and estimate their stellar properties and mass accretion rate (dM/dt). Our measurements represent the largest dM/dt data set of low-metallicity stars presented so far. As such, they offer a unique opportunity to study on a statistical basis the mass accretion process in the LMC and, more in general, the evolution of the mass accretion process around low-metallicity stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/690/512
- Title:
- LMXBs and globulars in early-type galaxies. II.
- Short Name:
- J/ApJ/690/512
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an astrometry and photometry catalogue of globular cluster (GC) candidates detected with the Hubble Space Telescope Wide Field Planetary Camera 2 in a sample of 19 early-type galaxies, appropriate for comparison with the low-mass X-ray binary populations observed with Chandra. In a companion paper (Cat. J/ApJ/689/983), we present the Chandra data and investigate the relation between these populations. We demonstrate that, although there is little evidence of a color-magnitude correlation for the GCs, after estimating mass and metallicity from the photometry under the assumption of a single-age simple stellar population, there is a significant positive correlation between mass and metallicity.
- ID:
- ivo://CDS.VizieR/J/AJ/133/394
- Title:
- Low-mass binary companions in M35
- Short Name:
- J/AJ/133/394
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Hubble Space Telescope Fine Guidance Sensors data on 23 stars in the intermediate-age cluster M35 having B-V<0.5 (~F7V) are analyzed to test whether binary periods, separations, and masses can be estimated by measuring periodic variations in the residuals of their internal proper motions. Of the 23 stars examined, 4 appear to possess a periodic signal. Unfortunately, these detections cannot be considered firm because the amplitudes of these waveforms are small (~1mas), the signal is only seen in one coordinate, and the derived periods are close to the duration of the data set. If the signals are real, they predict binary separations of >6AU, secondary masses between 0.3 and 0.6M_{sun}_, and mass ratios of about 0.2. This latter value is in agreement with capture models employing stars with circumstellar disks for the formation of binaries.
- ID:
- ivo://CDS.VizieR/J/AJ/157/22
- Title:
- Luminous and variable stars in NGC 2403 and M81
- Short Name:
- J/AJ/157/22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of spectroscopy and multi-wavelength photometry of luminous and variable star candidates in the nearby spiral galaxies NGC 2403 and M81. We discuss specific classes of stars, the Luminous Blue Variables (LBVs), B[e] supergiants (sgB[e]), and the high-luminosity yellow hypergiants. We identify two new LBV candidates, and three sgB[e] stars in M81. We also find that some stars that were previously considered LBV candidates are actually field stars. The confirmed and candidate LBVs and sgB[e] stars together with the other confirmed members are shown on the HR Diagrams for their respective galaxies. We also present the HR Diagrams for the two "SN impostors", V37 (SN2002kg) and V12 (SN1954J) in NGC 2403 and the stars in their immediate environments.
- ID:
- ivo://CDS.VizieR/J/ApJ/810/107
- Title:
- Lyman break galaxies and LAEs HST photometry
- Short Name:
- J/ApJ/810/107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present U_336_V_606_J_125_H_160_ follow-up Hubble Space Telescope (HST) observations of 16 z~3 candidate Lyman continuum (LyC) emitters in the HS1549+1919 field. With these data, we obtain high spatial-resolution photometric redshifts of all sub-arcsecond components of the LyC candidates in order to eliminate foreground contamination and identify robust candidates for leaking LyC emission. Of the 16 candidates, we find one object with a robust LyC detection that is not due to foreground contamination. This object (MD5) resolves into two components; we refer to the LyC-emitting component as MD5b. MD5b has an observed 1500 {AA} to 900 {AA} flux-density ratio of (F_UV_/F_LyC_)_obs_=4.0+/-2.0, compatible with predictions from stellar population synthesis models. Assuming minimal IGM absorption, this ratio corresponds to a relative (absolute) escape fraction of f_esc,rel_^MD5b^=75%-100% (f_esc,abs_^MD5b^=14%-19%). The stellar population fit to MD5b indicates an age of <~50 Myr, which is in the youngest 10% of the HST sample and the youngest third of typical z~3 Lyman break galaxies, and may be a contributing factor to its LyC detection. We obtain a revised, contamination-free estimate for the comoving specific ionizing emissivity at z=2.85, indicating (with large uncertainties) that star-forming galaxies provide roughly the same contribution as QSOs to the ionizing background at this redshift. Our results show that foreground contamination prevents ground-based LyC studies from obtaining a full understanding of LyC emission from z~3 star-forming galaxies. Future progress in direct LyC searches is contingent upon the elimination of foreground contaminants through high spatial-resolution observations, and upon acquisition of sufficiently deep LyC imaging to probe ionizing radiation in high-redshift galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/703/2033
- Title:
- Lyman-break galaxies (LBG) in the HUDF
- Short Name:
- J/ApJ/703/2033
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a sample of 407 z~3 Lyman break galaxies (LBGs) to a limiting isophotal u-band magnitude of 27.6mag in the Hubble Ultra Deep Field. The LBGs are selected using a combination of photometric redshifts and the u-band drop-out technique enabled by the introduction of an extremely deep u-band image obtained with the Keck I telescope and the blue channel of the Low Resolution Imaging Spectrometer. The Keck u-band image, totaling 9hr of integration time, has a 1{sigma} depth of 30.7mag/arcsec^2^, making it one of the most sensitive u-band images ever obtained. The u-band image also substantially improves the accuracy of photometric redshift measurements of ~50% of the z~3 LBGs, significantly reducing the traditional degeneracy of colors between z~3 and z~0.2 galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/755/154
- Title:
- Mass accretion rates from HST in the ONC
- Short Name:
- J/ApJ/755/154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The present observational understanding of the evolution of the mass accretion rates (dM/dt_acc_) in pre-main-sequence stars is limited by the lack of accurate measurements of dM/dt_acc_ over homogeneous and large statistical samples of young stars. Such observational effort is needed to properly constrain the theory of star formation and disk evolution. Based on Hubble Space Telescope/WFPC2 observations, we present a study of dM/dt_acc_ for a sample of ~700 sources in the Orion Nebula Cluster, ranging from the hydrogen-burning limit to M*~2M_{sun}_. We derive dM/dt_acc_ from both the U-band excess and the H{alpha} luminosity (L_H{alpha}_), after determining empirically both the shape of the typical accretion spectrum across the Balmer jump and the relation between the accretion luminosity (L_acc_) and L_H{alpha}_, which is L_acc_/L_{sun}_=(1.31+/-0.03).L_H{alpha}/L_{sun}_+(2.63+/-0.13). Given our large statistical sample, we are able to accurately investigate relations between dM/dt_acc_ and the parameters of the central star such as mass and age.
- ID:
- ivo://CDS.VizieR/J/ApJ/875/51
- Title:
- Mass accretion rates of PMS stars. VI. LH95 in LMC
- Short Name:
- J/ApJ/875/51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the accretion properties of low-mass stars in the LH 95 association within the Large Magellanic Cloud. Using noncontemporaneous wideband optical and narrowband H{alpha} photometry obtained with the Hubble Space Telescope, we identify 245 low-mass pre-main-sequence (PMS) candidates showing H{alpha} excess emission above the 4{sigma} level. We derive their physical parameters, including effective temperatures, luminosities, masses (M_*_), ages, accretion luminosities, and mass accretion rates (dM/dt_acc_). We identify two different stellar populations: younger than ~8Myr with median dM/dt_acc_~5.4x10^-8^M_{sun}_/yr (and M_*_~0.15-1.8M_{sun}_) and older than ~8Myr with median dM/dt_acc_~4.8x10^-9^M_{sun}_/yr (and M_*_~0.6-1.2M_{sun}_). We find that the younger PMS candidates are assembled in groups around Be stars, while older PMS candidates are uniformly distributed within the region without evidence of clustering. We find that dM/dt_acc_ in LH 95 decreases with time more slowly than what is observed in Galactic star-forming regions (SFRs). This agrees with the recent interpretation, according to which higher metallicity limits the accretion process in both rate and duration due to higher radiation pressure. The dM/dt_acc_-M_*_ relationship shows different behavior at different ages, becoming progressively steeper at older ages, indicating that the effects of mass and age on dM/dt_acc_ cannot be treated independently. With the aim to identify reliable correlations between mass, age, and dM/dt_acc_, we used a multivariate linear regression fit between these parameters for our PMS candidates. The comparison between our results and those obtained in other SFRs of our Galaxy and the Magellanic Clouds confirms the importance of the metallicity for the study of the dM/dt_acc_ evolution in clusters with different environmental conditions.
- ID:
- ivo://CDS.VizieR/J/ApJ/881/54
- Title:
- Masses of SNR progenitors in M83
- Short Name:
- J/ApJ/881/54
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We determine the ages of the young, resolved stellar populations at the locations of 237 optically identified supernova remnants in M83. These age distributions put constraints on the progenitor masses of the supernovae that produced 199 of the remnants. The other 38 show no evidence for having a young progenitor and are therefore good Type Ia SNR candidates. Starting from Hubble Space Telescope broadband imaging, we measured resolved stellar photometry of seven archival WFC3/UVIS fields in F336W, F438W, and F814W. We generate color-magnitude diagrams of the stars within 50pc of each SNR and fit them with stellar evolution models to obtain the population ages. From these ages we infer the progenitor mass that corresponds to the lifetime of the most prominent age within the past 50Myr. In this sample, there are 47 SNRs with best-fit progenitor masses >15M_{sun}_, and 5 of these are >15M_{sun}_ at 84% confidence. This is the largest collection of high-mass progenitors to date, including our highest-mass progenitor inference found so far, with a constraint of <8Myr. Overall, the distribution of progenitor masses has a power-law index of -3.0_-0.7_^+0.2^, steeper than Salpeter initial mass function (-2.35). It remains unclear whether the reason for the low number of high-mass progenitors is due to the difficulty of finding and measuring such objects or because only a fraction of very massive stars produce supernovae.
