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Register a new userThe Galactic O-Star Spectroscopic Survey (GOSSS). II. Bright Southern Stars
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Jes\\'us Ma\\'iz Apell\\'aniz
Publication date
2013
fields
Physics
and research's language is
English
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We present the second installment of GOSSS, a massive spectroscopic survey of Galactic O stars, based on new homogeneous, high signal-to-noise ratio, R ~ 2500 digital observations from both hemispheres selected from the Galactic O-Star Catalog (GOSC). In this paper we include bright stars and other objects drawn mostly from the first version of GOSC, all of them south of delta = -20 degrees, for a total number of 258 O stars. We also revise the northern sample of paper I to provide the full list of spectroscopically classified Galactic O stars complete to B = 8, bringing the total number of published GOSSS stars to 448. Extensive sequences of exceptional objects are given, including the early Of/WN, O Iafpe, Ofc, ON/OC, Onfp, Of?p, and Oe types, as well as double/triple-lined spectroscopic binaries. The new spectral subtype O9.2 is also discussed. The magnitude and spatial distributions of the observed sample are analyzed. We also present new results from OWN, a multi-epoch high-resolution spectroscopic survey coordinated with GOSSS that is assembling the largest sample of Galactic spectroscopic massive binaries ever attained. The OWN data combined with additional information on spectroscopic and visual binaries from the literature indicate that only a very small fraction (if any) of the stars with masses above 15-20 M_Sol are born as single systems. In the future we will publish the rest of the GOSSS survey, which is expected to include over 1000 Galactic O stars.
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This is the third installment of GOSSS, a massive spectroscopic survey of Galactic O stars, based on new homogeneous, high signal-to-noise ratio, R~2500 digital observations selected from the Galactic O-Star Catalog (GOSC). In this paper we present 142 additional stellar systems with O stars from both hemispheres, bringing the total of O-type systems published within the project to 590. Among the new objects there are 20 new O stars. We also identify 11 new double-lined spectroscopic binaries (SB2s), of which 6 are of O+O type and 5 of O+B type, and an additional new tripled-lined spectroscopic binary (SB3) of O+O+B type. We also revise some of the previous GOSSS classifications, present some egregious examples of stars erroneously classified as O-type in the past, introduce the use of luminosity class IV at spectral types O4-O5.5, and adapt the classification scheme to the work of Arias et al. (2016).
The Galactic O-Star Spectroscopic Survey (GOSSS) is obtaining high quality R~2500 blue-violet spectroscopy of all Galactic stars ever classified as of O type with B < 12 and a significant fraction of those with B = 12-14. As of June 2013, we have obtained, processed, and classified 2653 spectra of 1593 stars, including all of the sample with B < 8 and most of the sample with B = 8-10, making GOSSS already the largest collection of high quality O-star optical spectra ever assembled by a factor of 3. We discuss the fraction of false positives (stars classified as O in previous works that do not belong to that class) and the implications of the observed magnitude distribution for the spatial distribution of massive stars and dust within a few kpc of the Sun. We also present new spectrograms for some of the interesting objects in the sample and show applications of GOSSS data to the study of the intervening ISM. Finally, we present the new version of the Galactic O-Star Catalog (GOSC), which incorporates the data in GOSSS-DR1, and we discuss our plans for MGB, an interactive spectral classification tool for OB stars.
Besides monitoring the bright star $beta$ Pic during the near transit event for its giant exoplanet, the $beta$ Pictoris b Ring (bRing) observatories at Siding Springs Observatory, Australia and Sutherland, South Africa have monitored the brightnesses of bright stars ($V$ $simeq$ 4--8 mag) centered on the south celestial pole ($delta$ $leq$ -30$^{circ}$) for approximately two years. Here we present a comprehensive study of the bRing time series photometry for bright southern stars monitored between 2017 June and 2019 January. Of the 16762 stars monitored by bRing, 353 of them were found to be variable. Of the variable stars, 80% had previously known variability and 20% were new variables. Each of the new variables was classified, including 3 new eclipsing binaries (HD 77669, HD 142049, HD 155781), 26 $delta$ Scutis, 4 slowly pulsating B stars, and others. This survey also reclassified four stars based on their period of pulsation, light curve, spectral classification, and color-magnitude information. The survey data were searched for new examples of transiting circumsecondary disk systems, but no candidates were found.
With both nebular- and stellar-derived abundances of $lesssim$ 1/10 Zsun and low foreground extinction, Sextans A is a prime candidate to replace the Small Magellanic Cloud as reservoir of metal-poor massive stars and reference to study the metal-poor Universe. We report the discovery of two early-O type stars in Sextans A, the earliest O-stars with metallicity < 1/7 Zsun known to date, and two additional O9 stars. Colour-excess estimates towards individual targets, enabled by spectral typing, manifest that internal reddening is neither uniform nor negligible. The four targets define a new region of star formation far from the optically-brightest centre of the galaxy and from its conspicuous HII shells, but not devoid of neutral hydrogen. In fact, we detect a spatial correlation between OB-stars and HI in Sextans A and other dIrrs that leads us to propose that the neutral phase may be fundamental to star formation in low-density environments. According to the existing evidence at least two of the targets formed in isolation, thus suggestive of an stochastic sampling of the initial mass function that would enable low-mass galaxies like Sextans A to form very massive stars. The discovery of these four stars provide spatially-resolved, spectroscopic confirmation of recent findings suggesting that dwarf galaxies can sustain star formation despite the low density of the gas phase.
In this work, we present a spectroscopic study of very massive stars found outside the center of the massive stellar cluster NGC3603. From the analysis of SOAR spectroscopic data and related optical-NIR photometry, we confirm the existence of several very massive stars in the periphery of NGC 3603. The first group of objects (MTT58, WR42e and RFS7) is compound by three new Galactic exemplars of the OIf*/WN type, all of them with probable initial masses well above 100 Msun and estimated ages of about 1 Myr. Based on Goodman blue-optical spectrum of MTT68, we can confirm the previous finding in the NIR of the only other Galactic exemplar (besides HD93129A) of the O2If* type known to date. Based on its position relative to a set of theoretical isochrons in a Hertzprung-Russel diagram, we concluded that the new O2If* star could be one of the most massive (150 Msun) and luminous (Mv=-7.3) O-star in the Galaxy. Also, another remarkable result is the discovery of a new O2V star (MTT31) that is the first exemplar of the class so far identified in the Milk Way. From its position in the Hertzprung-Russel diagram it is found that this new star probably had an initial mass of 80 Msun, as well as an absolute magnitude Mv=-6.0 corresponding to a luminosity similar to other known O2V stars in the LMC. We also communicate the discovery of a new Galactic O3.5If* star (RFS8) which case is quite intriguing. Indeed, It is located far to the south of the NGC 3603 center, in apparent isolation at a large radial projected linear distance of 62 pc. Its derived luminosity is similar to that of the other O3.5If* (Sh18) found in the NGC 3603s innermost region. The fact that a such high mass star is observed far isolated in the field led us to speculate that perhaps it could have been expelled from the innermost parts of the complex by a close fly-by dynamical encounter with a very massive hard binary system.
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