The Galactic O-Star Spectral Survey (GOSSS) Alfredo Sota; Jesús Maíz-Apellániz; Rodolfo H. Barbá ...
Bulletin de la Société royale des sciences de Liège,
01/2011, Letnik:
80
Journal Article
Recenzirano
Odprti dostop
The Galactic O-Star Spectroscopic Survey (GOSSS) is a project that is observing all known Galactic O stars with B < 13 (+/-2000 objects) in the blue-violet part of the spectrum with R+/-2500. It also ...includes two companion surveys (a spectroscopic one at R+/-1500 and a high resolution imaging one). It is based on v2.0 of the Galactic O star catalog (v1, Maíz-Apellániz et al. 2004; v2, Sota et al. 2008). We have completed the first part of the main project. Here we present results on the first 400 objects of the sample.
We present the analysis of high-resolution optical spectroscopic observations of the zero-age main-sequence O star Herschel 36 spanning six years. This star is definitely a multiple system, with at ...least three components detected in its spectrum. Based on our radial-velocity (RV) study, we propose a picture of a close massive binary and a more distant companion, most probably in wide orbit about each other. The orbital solution for the binary, whose components we identify as O9 V and B0.5 V, is characterized by a period of 1.5415 {+-} 0.0006 days. With a spectral type O7.5 V, the third body is the most luminous component of the system and also presents RV variations with a period close to 498 days. Some possible hypotheses to explain the variability are briefly addressed and further observations are suggested.
We are carrying out a bibliographic compilation of near-infrared (NIR)(0.7-5.0 um) spectroscopic studies available for stars in the Galactic O Star Catalog (GOSC, Maíz Apellániz et al. 2004). This ...compilation allows us to quantify the precise degree of knowledge about NIR spectral information for GOSC sources, such as band coverage, spectral resolution, equivalent-width measurements, etc. This bibliographic compilation has a clear next step toward the development of a new catalog of O-type stars observed only in the NIR, which will be annexed to the GOSC. In this poster paper we present preliminary results derived from a set of different attributes extracted from the retrieved papers.
We use deep multi-epoch near-IR images of the VISTA Variables in the Vía Láctea (VVV) Survey to search for RR Lyrae stars towards the Southern Galactic plane. Here we report the discovery of a group ...of RR Lyrae stars close together in VVV tile d025. Inspection of the VVV images and PSF photometry reveals that most of these stars are likely to belong to a globular cluster, that matches the position of the previously known star cluster FSR\,1716. The stellar density map of the field yields a \(>100\) sigma detection for this candidate globular cluster, that is centered at equatorial coordinates \(RA_{J2000}=\)16:10:30.0, \(DEC_{J2000}=-\)53:44:56; and galactic coordinates \(l=\)329.77812, \(b=-\)1.59227. The color-magnitude diagram of this object reveals a well populated red giant branch, with a prominent red clump at \(K_s=13.35 \pm 0.05\), and \(J-K_s=1.30 \pm 0.05\). We present the cluster RR Lyrae positions, magnitudes, colors, periods and amplitudes. The presence of RR Lyrae indicates an old globular cluster, with age \(>10\) Gyr. We classify this object as an Oosterhoff type I globular cluster, based on the mean period of its RR Lyrae type ab, \( =0.540\) days, and argue that this is a relatively metal-poor cluster with \(Fe/H = -1.5 \pm 0.4\) dex. The mean extinction and reddening for this cluster are \(A_{K_s}=0.38 \pm 0.02\), and \(E(J-K_s)=0.72 \pm 0.02\) mag, respectively, as measured from the RR Lyrae colors and the near-IR color-magnitude diagram. We also measure the cluster distance using the RR Lyrae type ab stars. The cluster mean distance modulus is \((m-M)_0 = 14.38 \pm 0.03\) mag, implying a distance \(D = 7.5 \pm 0.2\) kpc, and a Galactocentric distance \(R_G=4.3\) kpc.
We present, for the first time, an optical spectroscopic data cube of the giant star-forming region 30 Doradus, obtained with the GIRAFFE on the VLT at Paranal Observatory. The main emission lines ...present in this data cube correspond to H{\alpha}, NII 6548 Å and NII 6584 Å. By using this data set, we found that H{\alpha} presents from simple to multiple profiles, which suggests that different physical mechanisms act in different ways on the excited gas in 30 Doradus. We found, at least, three unclassified large expanding structures. These structures correlate with peaks in the X-ray distribution. Given the excellent signal-to-noise ratio and the large spatial coverage of this data cube, we have studied in detail the kinematics of 30 Doradus, showing the importance of the small scale phenomena on the integrated properties of 30 Doradus.
Aims: We search for direct evidence of ongoing star formation by accretion in the Lagoon Nebula (M8), using optical wide-field narrow-band imaging obtained at La Silla Observatory. Methods: We ...examine SII and Halpha images for line-emission features that could be interpreted as signatures of outflow activity of the exciting sources. Results: We discover five new Herbig-Haro objects, study in detail their morphology and attempt to identify their potential driving sources among the population of T Tauri stars and embedded sources in the surroundings. Conclusions: The results reported here conclusively demonstrate the existence of very young stars going through the accreting phase in the M8 region.
Extremely broad emission wings at H\(\beta\) and H\(\alpha\) have been found in VFTS 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 H\(\beta\) and the shortward wing of H\(\alpha\). 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. 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.
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 S3MC infrared imaging ...survey as showing an excess of emission at 24 um indicative of warm dust, such as that associated with a transitional or debris disks. We use these long-slit spectra to investigate the origin of the 24 um emission and the nature of these stars. A possible explanation for the observed 24 um excess, that these are emission line stars with dusty excretion disks, is disproven for the majority of our sources. 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 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 stars with forbidden-line emission. We discover a new O6 Iaf star; it exhibits strong HeII 4686 A emission but relatively weak NIII 4640 A emission that we attribute to the lower nitrogen abundance in the SMC. Two other objects are identified with planetary nebulae, one with a young stellar object, and two with X-ray binaries. To shed additional light on the nature of the observed 24 um excess we use optical and infrared photometry to estimate the dust properties of the objects with normal O and B star spectra and compare these properties to those of a sample of hot spots in the Galactic interstellar medium (ISM). We find that the dust properties of the dusty OB star sample resemble the properties of the Galactic sample of hot spots. Some may be runaway systems with bow-shocks resulting from a large velocity difference between star and ISM. We further investigate the nature of these dusty OB stars in a companion paper presenting mid-infrared spectroscopy and additional imaging.
PDF