Star Formation in 30 Doradus De Marchi, Guido; Paresce, Francesco; Panagia, Nino ...
The Astrophysical journal,
09/2011, Letnik:
739, Številka:
1
Journal Article
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Using observations obtained with the Wide-Field Camera 3 on board the Hubble Space Telescope, we have studied the properties of the stellar populations in the central regions of 30 Dor in the Large ...Magellanic Cloud. The observations clearly reveal the presence of considerable differential extinction across the field. We characterize and quantify this effect using young massive main-sequence stars to derive a statistical reddening correction for most objects in the field. We then search for pre-main-sequence (PMS) stars by looking for objects with a strong (>4 Delta *s) H Delta *a excess emission and find about 1150 of them over the entire field. Comparison of their location in the Hertzsprung-Russell diagram with theoretical PMS evolutionary tracks for the appropriate metallicity reveals that about one-third of these objects are younger than ~4 Myr, compatible with the age of the massive stars in the central ionizing cluster R 136, whereas the rest have ages up to ~30 Myr, with a median age of ~12 Myr. This indicates that star formation has proceeded over an extended period of time, although we cannot discriminate between an extended episode and a series of short and frequent bursts that are not resolved in time. While the younger PMS population preferentially occupies the central regions of the cluster, older PMS objects are more uniformly distributed across the field and are remarkably few at the very center of the cluster. We attribute this latter effect to photo-evaporation of the older circumstellar disks caused by the massive ionizing members of R 136.
How Dark the Sky: The JWST Backgrounds Rigby, Jane R.; Lightsey, Paul A.; García Marín, Macarena ...
Publications of the Astronomical Society of the Pacific,
04/2023, Letnik:
135, Številka:
1046
Journal Article
Using HST ACS, we have obtained deep optical images reaching stars well below the oldest main-sequence turnoff in the spheroid, tidal stream, and outer disk of Andromeda. We have reconstructed the ...star formation history in these fields by comparing their color-magnitude diagrams to a grid of isochrones calibrated to Galactic globular clusters observed in the same bands. Each field exhibits an extended star formation history, with many stars younger than 10 Gyr but few younger than 4 Gyr. Considered together, the star counts, kinematics, and population characteristics of the spheroid argue against some explanations for its intermediate-age, metal-rich population, such as a significant contribution from stars residing in the disk or a chance intersection with the stream's orbit. Instead, it is likely that this population is intrinsic to the inner spheroid, whose highly disturbed structure is clearly distinct from the pressure-supported metal-poor halo that dominates farther from the galaxy's center. The stream and spheroid populations are similar, but not identical, with the stream's mean age being 61 Gyr younger; this similarity suggests that the inner spheroid is largely polluted by material stripped from either the stream's progenitor or similar objects. The disk population is considerably younger and more metal-rich than the stream and spheroid populations, but not as young as the thin-disk population of the solar neighborhood; instead, the outer disk of Andromeda is dominated by stars of age 4-8 Gyr, resembling the Milky Way's thick disk. The disk data are inconsistent with a population dominated by ages older than 10 Gyr and in fact do not require any stars older than 10 Gyr.
The newly installed Wide Field Camera 3 (WFC3) on the Hubble Space Telescope has been used to obtain multi-band images of the nearby spiral galaxy M83. These new observations are the deepest and ...highest resolution images ever taken of a grand-design spiral, particularly in the near-ultraviolet, and allow us to better differentiate compact star clusters from individual stars and to measure the luminosities of even faint clusters in the U band. We find that the luminosity function (LF) for clusters outside of the very crowded starburst nucleus can be approximated by a power law, dN/dL {proportional_to} L {sup {alpha}}, with {alpha} = -2.04 {+-} 0.08, down to M{sub V} {approx} -5.5. We test the sensitivity of the LF to different selection techniques, filters, binning, and aperture correction determinations, and find that none of these contribute significantly to uncertainties in {alpha}. We estimate ages and masses for the clusters by comparing their measured UBVI, H{alpha} colors with predictions from single stellar population models. The age distribution of the clusters can be approximated by a power law, dN/d{tau} {proportional_to} {tau}{sup {gamma}}, with {gamma} = -0.9 {+-} 0.2, for M {approx}> few x 10{sup 3} M {sub sun} and {tau} {approx}< 4 x 10{sup 8} yr. This indicates that clusters are disrupted quickly, with {approx}80%-90% disrupted each decade in age over this time. The mass function of clusters over the same M-{tau} range is a power law, dN/dM {proportional_to} M {sup {beta}}, with {beta} = -1.94 {+-} 0.16, and does not have bends or show curvature at either high or low masses. Therefore, we do not find evidence for a physical upper mass limit, M{sub C} , or for the earlier disruption of lower mass clusters when compared with higher mass clusters, i.e., mass-dependent disruption. We briefly discuss these implications for the formation and disruption of the clusters.
Early Release Science observations of the cluster NGC 3603 with the WFC3 on the refurbished Hubble Space Telescope allow us to study its recent star formation history. Our analysis focuses on stars ...with H{alpha} excess emission, a robust indicator of their pre-main sequence (PMS) accreting status. The comparison with theoretical PMS isochrones shows that 2/3 of the objects with H{alpha} excess emission have ages from 1 to 10 Myr, with a median value of 3 Myr, while a surprising 1/3 of them are older than 10 Myr. The study of the spatial distribution of these PMS stars allows us to confirm their cluster membership and to statistically separate them from field stars. This result establishes unambiguously for the first time that star formation in and around the cluster has been ongoing for at least 10-20 Myr, at an apparently increasing rate.
Using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, we have obtained deep, far-ultraviolet images of the compact elliptical galaxy M32. When combined with earlier ...near-ultraviolet images of the same field, these data enable the construction of an ultraviolet color- magnitude diagram of the hot horizontal branch (HB) population and other hot stars in late phases of stellar evolution. We find few post-asymptotic giant branch (PAGB) stars in the galaxy, implying that these stars either cross the H-R diagram more rapidly than expected, and/or that they spend a significant fraction of their time enshrouded in circumstellar material. The predicted luminosity gap between the hot HB and its AGB-manque (AGBM) progeny is less pronounced than expected, especially when compared to evolutionary tracks with enhanced helium abundances, implying that the presence of hot HB stars in this metal-rich population is not due to image. Only a small fraction (image2%) of the HB population is hot enough to produce significant UV emission, yet most of the UV emission in this galaxy comes from the hot HB and AGBM stars, implying that PAGB stars are not a significant source of UV emission, even in those elliptical galaxies with a weak UV excess.
We present Wide Field Camera 3 images taken with the Hubble Space Telescope within a single field in the southern grand design star-forming galaxy M83. Based on their size, morphology, and photometry ...in continuum-subtracted Halpha, S II, Hbeta, O III, and O II filters, we have identified 60 supernova remnant (SNR) candidates, as well as a handful of young ejecta-dominated candidates. A catalog of these remnants, their sizes and, where possible, their Halpha fluxes are given. Radiative ages and pre-shock densities are derived from those SNRs that have good photometry. The ages lie in the range 2.62 < log (tau{sub rad}/yr) < 5.0, and the pre-shock densities at the blast wave range over 0.56 < n{sub 0}/cm{sup -3} < 1680. Two populations of SNRs have been discovered. These divide into a nuclear and spiral arm group and an inter-arm population. We infer an arm to inter-arm density contrast of 4. The surface flux in diffuse X-rays is correlated with the inferred pre-shock density, indicating that the warm interstellar medium (ISM) is pressurized by the hot X-ray plasma. We also find that the ISM in the nuclear region of M83 is characterized by a very high porosity and pressure, and infer an SNR rate of 1 per 70-150 yr for the nuclear (R < 300 pc) region. On the basis of the number of SNRs detected and their radiative ages, we infer that the lower mass of Type II SNe in M83 is M{sub min} = 16{sup +7}{sub -5} M{sub sun}. Finally, we give evidence for the likely detection of the remnant of the historical supernova, SN1968L.
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