We present the results from the quantitative spectroscopic analysis of ~280 likely single O stars targeted by the IACOB and OWN surveys. This implies the largest sample of Galactic O-type stars ...analyzed homogeneously to date. We used the iacob-broad and iacob-gbat tools (see Simón-Díaz et al. 2011,2015) to obtain the complete set of spectroscopic parameters which can be determined from the optical spectrum of O-type stars: projected rotational velocity (v sin i), macroturbulence velocity (v
mac), effective temperature (T
eff), gravity (logg), wind-strength (logQ), helium abundance (Y
He), microturbulence (ξt), and the exponent of the wind-law (β).
We present the first high-spatial-resolution near-infrared (NIR) imaging of NGC604, obtained with the NICMOS camera onboard the
Hubble Space Telescope (HST)
. These NICMOS broad-band images reveal ...new NIR point sources, clusters, and diffuse structures. We find an excellent spatial correlation between the 8.4 GHz radio continuum and the 2.2 μm nebular emission. Moreover, massive young stellar object candidates appear aligned with these radio peaks, reinforcing the idea that those areas are star-forming regions. Three different scaled OB associations are recognized in the NICMOS images. The brightest NIR sources in our images have properties that suggest that they are red supergiant stars, of which one was previously known. This preliminary analysis of the NICMOS images shows the complexity of the stellar content of the NGC604 nebula.
The massive Wolf-Rayet stellar system HD 5980 in the Small Magellanic Cloud entered a sudden and brief ~ 1-3 mag eruptive state in the mid-1990s. The cause of the instability is not yet understood, ...but mechanisms similar to those in luminous blue variables are suspected. Using a previously unreported set of spectroscopic data obtained in 1955-1967 and recently acquired optical and HST/STIS spectra, we find that (1) the brief eruptions of 1993 and 1994 occurred at the beginning of an extended (~ decades) high state of activity characterized by large emission-line intensities; (2) the level of activity is currently subsiding; and (3) another strong emission-line episode appears to have occurred between 1960 and 1965, suggesting the possibility that the long-term cyclical variability may be recurrent on a ~ 40 year timescale. These characteristics suggest the possible classification of HD 5980 as an S Doradus-type variable. The effects due to binary interactions in the system are discussed, and we tentatively suggest that the short duration and relatively hot spectral type (WN11/B1.5I) observed during maximum in the visual light curve may be attributed to these interactions.
A deep dive into NGC 604 with Gemini/NIRI imaging Fariña, Cecilia; Bosch, Guillermo L.; Barbá, Rodolfo R.
Proceedings of the International Astronomical Union,
08/2009, Letnik:
5, Številka:
S266
Journal Article
Recenzirano
Odprti dostop
The giant Hii region NGC 604 constitutes a complex and rich population to study in detail many aspects of massive star formation, such as their environments and physical conditions, the evolutionary ...processes involved, the initial mass function for massive stars and star-formation rates, among many others. Here, we present our first results of a near-infrared study of NGC 604 performed with NIRI images obtained with Gemini North. Based on deep JHK photometry, 164 sources showing infrared excess were detected, pointing to the places where we should look for star-formation processes currently taking place. In addition, the color–color diagram reveals a great number of objects that could be giant/supergiant stars or unresolved, small, tight clusters. An extinction map obtained based on narrow-band images is also shown.
Many problems in contemporary astrophysics-from understanding the formation of black holes to untangling the chemical evolution of galaxies-rely on knowledge about binary stars. This, in turn, ...depends on the discovery and characterization of binary companions for large numbers of different kinds of stars in different chemical and dynamical environments. Current stellar spectroscopic surveys observe hundreds of thousands to millions of stars with (typically) few observational epochs, which allows for binary discovery but makes orbital characterization challenging. We use a custom Monte Carlo sampler (The Joker) to perform discovery and characterization of binary systems through radial velocities, in the regime of sparse, noisy, and poorly sampled multi-epoch data. We use it to generate posterior samplings in Keplerian parameters for 232,495 sources released in APOGEE Data Release 16. Our final catalog contains 19,635 high-confidence close-binary (P few years, a few ) systems that show interesting relationships between binary occurrence rate and location in the color-magnitude diagram. We find notable faint companions at high masses (black hole candidates), at low masses (substellar candidates), and at very close separations (mass-transfer candidates). We also use the posterior samplings in a (toy) hierarchical inference to measure the long-period binary-star eccentricity distribution. We release the full set of posterior samplings for the entire parent sample of 232,495 stars. This set of samplings involves no heuristic "discovery" threshold and therefore can be used for myriad statistical purposes, including hierarchical inferences about binary-star populations and subthreshold searches.
Abstract
APOGEE spectra offer ≲1 km s
−1
precision in the measurement of stellar radial velocities. This holds even when multiple stars are captured in the same spectrum, as happens most commonly ...with double-lined spectroscopic binaries (SB2s), although random line-of-sight alignments of unrelated stars can also occur. We develop a code that autonomously identifies SB2s and higher order multiples in the APOGEE spectra, resulting in 7273 candidate SB2s, 813 SB3s, and 19 SB4s. We estimate the mass ratios of binaries, and for a subset of these systems with a sufficient number of measurements we perform a complete orbital fit, confirming that most systems with periods of <10 days have circularized. Overall, we find an SB2 fraction (
F
SB2
) ∼ 3% among main-sequence dwarfs, and that there is not a significant trend in
F
SB2
with temperature of a star. We are also able to recover a higher
F
SB2
in sources with lower metallicity, however there are some observational biases. We also examine light curves from TESS to determine which of these spectroscopic binaries are also eclipsing. Such systems, particularly those that are also pre- and post-main sequence, are good candidates for a follow-up analysis to determine their masses and temperatures.
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