We present Hubble Space Telescope Wide Field Planetary Camera 2 images of a prominent externally ionized molecular globule in the Carina Nebula (NGC 3372), supplemented with ground-based infrared ...images and visual-wavelength spectra. This molecular globule has a shape resembling a human hand, with an extended finger that points toward its likely source of ionizing radiation. Following an analysis of the spatially resolved ionization structure and spectrum of the photoevaporative flow from the Finger, we conclude that the dominant ionizing source is either the WNL star WR25 (HD 93162), the adjacent O4 If-type star Tr16-244, or perhaps both. We estimate a mass-loss rate of ∼2 × 10−5 M⊙ yr−1 from the main evaporating surface of the globule, suggesting a remaining lifetime of 105.3–106 yr. We find a total mass for the entire globule of more than 6 M⊙, in agreement with previous estimates. The hydrogen column density through the globule derived from extinction measurements is a few times 1022 cm−2, so the photodissociation region behind the ionization front should be limited to a thin layer compared to the size of the globule, in agreement with the morphology seen in H2 images. Although a few reddened stars are seen within the boundary of the globule in near-infrared continuum images, these may be background stars. We do not detect a reddened star at the apex of the finger, for example, down to a limiting magnitude of mK≃ 17. However, considering the physical properties of the globule and the advancing ionization front, it appears that future star formation is likely in the Finger globule, induced by radiation-driven implosion.
We present the results of optical spectroscopic follow-up of 125 candidate main sequence OB stars in the Small Magellanic Cloud (SMC) that were originally identified in the S super(3)MC infrared ...imaging survey as showing an excess of emission at 24 mu m indicative of warm dust, such as that associated with a transitional or debris disks. We find that 88 of these objects are normal stars without line emission, with spectral types mostly ranging from late-O to early-B; luminosity classes from the literature for a sub-set of our sample indicate that most are main-sequence stars. We further identify 17 emission-line stars, 7 possible emission-line stars, and 5 other objects with forbidden-line emission in our sample. We find that the dust properties of the dusty OB star sample resemble the properties of the Galactic sample of hot spots. We further investigate the nature of these dusty OB stars in a companion paper presenting mid-infrared spectroscopy and additional imaging.
ABSTRACT Extremely broad emission wings at Hβ and H have been found in VLT-FLAMES Tarantula Survey data for five very luminous BA supergiants in or near 30 Doradus in the Large Magellanic Cloud. The ...profiles of both lines are extremely asymmetrical, which we have found to be caused by very broad diffuse interstellar bands (DIBs) in the longward wing of Hβ and the shortward wing of H . These DIBs are well known to interstellar but not to many stellar specialists, so that the asymmetries may be mistaken for intrinsic features. The broad emission wings are generally ascribed to electron scattering, although we note difficulties for that interpretation in some objects. Such profiles are known in some Galactic hyper/supergiants and are also seen in both active and quiescent Luminous Blue Variables (LBVs). No prior or current LBV activity is known in these 30 Dor stars, although a generic relationship to LBVs is not excluded; subject to further observational and theoretical investigation, it is possible that these very luminous supergiants are approaching the LBV stage for the first time. Their locations in the HRD and presumed evolutionary tracks are consistent with that possibility. The available evidence for spectroscopic variations of these objects is reviewed, while recent photometric monitoring does not reveal variability. A search for circumstellar nebulae has been conducted, with an indeterminate result for one of them.
In this work we present high resolution spectroscopic data of the giant star-forming region of N11, obtained with the GIRAFFE instrument at the Very Large Telescope. By using this data set, we find ...that most of the Hα emission lines profiles in this complex can be fitted by a single Gaussian, however, multiple emission line profiles can be observed in the central region of N11. By adding all the spectra, we derive the integrated Hα profile of this complex, which displays a width (σ) of about 12 km s−1 (corrected by instrumental and thermal width). We find that a single Gaussian fit on the integrated Hα profile leaves remaining wings, which can be fitted by a secondary broad Gaussian component. In addition, we find high velocity features, which spatially correlate with soft diffuse X-ray emission.
We present the physical characterization of FSR 1758, a new large, massive object very recently discovered in the Galactic Bulge. The combination of optical data from the 2nd Gaia Data Release and ...the DECam Plane Survey and near-IR data from the VISTA Variables in the Vía Láctea Extended Survey led to a clean sample of likely members. Based on this integrated data set, position, distance, reddening, size, metallicity, absolute magnitude, and proper motion (PM) of this object are measured. We estimate the following parameters: = 17:31:12, δ = −39:48:30 (J2000), D = 11.5 1.0 kpc, mag, Rc = 10 pc, Rt = 150 pc, dex, Mi < −8.6 1.0, = −2.85 mas yr−1, and δ = 2.55 mas yr−1. The nature of this object is discussed. If FRS 1758 is a genuine globular cluster (GC), it is one of the largest in the Milky Way, with a size comparable or even larger than that of Cen, being also an extreme outlier in the size versus Galactocentric distance diagram. The presence of a concentration of long-period RR Lyrae variable stars and blue horizontal branch stars suggests that it is a typical metal-poor GC of Oosterhoff type II. Further exploration of a larger surrounding field reveals common PM stars, suggesting either tidal debris or that FRS 1758 is actually the central part of a larger extended structure such as a new dwarf galaxy, tentatively named Scorpius. In either case, this object is remarkable, and its discovery graphically illustrates the possibility of finding other large objects hidden in the Galactic Bulge using future surveys.
The relatively nearby star-forming complex G305 is one of the most luminous H ii regions in the Galaxy, and it contains several sites and epochs of star formation. Using a combination of ...near-infrared photometry from "Vista Variables in Via Lactea" ESO Large Public Survey, SDSS-IV APOGEE-2 spectra, and Gaia DR2 photometry and astrometry, we report on 29 OB type, Wolf-Rayet, and emission-line stars, 18 of which are newly classified. Most of these hot stars belongs to the main sequence, although some stars of class I are also proposed. The mean radial velocity is RV = −41.8 . The average spectroscopic distance is 3.2 1.6 kpc, while the Gaia DR2 average distance is 3.7 1.8 kpc. Eight objects show light-curve variations with amplitudes greater than 0.5 mag in the KS band.
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