The OB Stars—Nolan R. Walborn

A deep objective-prism survey for Hα emission stars towards the Canis Major star-forming clouds was performed. A total of 398 Hα emitters were detected, 353 of which are new detections. There is a strong concentration of these Hα emitters towards the molecular clouds surrounding the CMa OB1 association, and it is likely that these stars are young stellar objects recently born in the clouds. An additional population of Hα emitters is scattered all across the region, and probably includes unrelated foreground dMe stars and background Be stars. About 90% of the Hα emitters are detected by WISE, of which 75% was detected with usable photometry. When plotted in a WISE colour–colour diagram it appears that the majority are Class II YSOs. Coordinates and finding charts are provided for all the new stars, and coordinates for all the detections. We searched the Gaia-DR2 catalogue and from 334 Hα emission stars with useful parallaxes, we selected a subset of 98 stars that have parallax errors of less than 20% and nominal distances in the interval 1050 to 1350 pc that surrounds a strong peak at 1185 pc in the distance distribution. Similarly, Gaia distances were obtained for 51 OB-stars located towards Canis Major and selected with the same parallax errors as the Hα stars. We find a median distance for the OB stars of 1182 pc, in excellent correspondence with the distance from the Hα stars. Two known runaway stars are confirmed as members of the association. Finally, two new Herbig-Haro objects are identified.

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Distribution of OB stars and absorbing matter in the region around P Cyg

Astrophysics ◽

10.1007/bf01005823 ◽

1984 ◽

Vol 20 (2) ◽

pp. 129-138 ◽

Cited By ~ 1

Author(s):

A. T. Garibdzhanyan ◽

K. G. Gasparyan ◽

R. Kh. Oganesyan

Keyword(s):

Ob Stars

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Multivariate statistical analysis of OB stars around h and ? Persei

Astrophysics ◽

10.1007/bf01006008 ◽

1988 ◽

Vol 27 (2) ◽

pp. 484-488

Author(s):

L. G. Balazs ◽

A. T. Garibdzhanyan

Keyword(s):

Statistical Analysis ◽

Multivariate Statistical Analysis ◽

Multivariate Statistical ◽

Ob Stars

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New Results on Pulsating OB Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100036769 ◽

1995 ◽

Vol 155 ◽

pp. 44-55 ◽

Cited By ~ 1

Author(s):

Paweł Moskalik

Keyword(s):

Data Model ◽

Physical Mechanism ◽

High Order ◽

Early Type ◽

Instability Strip ◽

Model Calculations ◽

B Stars ◽

Ob Stars ◽

Early Type Stars ◽

Theoretical Results

AbstractUntil very recently the physical mechanism driving oscillations in β Cep and other early type stars has been a mystery. The breakthrough came with the publication of new OPAL and OP opacity data. Model calculations with the new opacities have demonstrated that the pulsations are driven by the familiar K-mechanism, acting in the metal opacity bump at T ≈ 2 × 105K. The mechanism excites the low order p- and g-modes in the upper part of the instability strip and the high order g-modes in the lower part of the strip. The theoretical instability domains agree well with the observed domains of the β Cep and the SPB stars. In this review I present these recent theoretical results and discuss their consequences for our understanding of B stars pulsations.

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Dredge-up by Sound Wave Emission from a Convective Core

International Astronomical Union Colloquium ◽

10.1017/s0252921100093556 ◽

1988 ◽

Vol 108 ◽

pp. 99-100

Author(s):

Masa-aki Kondo

Keyword(s):

Spherical Harmonics ◽

Sound Wave ◽

Sound Waves ◽

Bottom Boundary ◽

Ob Stars ◽

Nonradial Oscillation ◽

Convective Core ◽

Propagation Zone ◽

Wave Emission ◽

Upper Boundary

Concerning the scattering of OB stars in the HR diagram (Humphry 1980), the effects of overshooting of convective core (Maeder 1984), mass loss (cf. chiosi and Maeder 1986), and generous stability criterion of semi-convection (Stothers and Chin 1976) have been discussed. Here, we will note the dredge up effect is caused by the sound waves emitted from a convective core.The sound mode of nonradial oscillation, with the spherical harmonics Ylm(θ, ϕ) and the frequency ω, can exist in the propagation zone, where the bottom boundary locates at the position of , and the upper boundary does near the photosphere. Here, Ll is called as the Lamb frequency, and cs is the sound velocity.

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Dark dust and single-cloud sightlines in the ISM

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037511 ◽

2020 ◽

Vol 641 ◽

pp. A35

Author(s):

R. Siebenmorgen ◽

J. Krełowski ◽

J. Smoker ◽

G. Galazutdinov ◽

S. Bagnulo

Keyword(s):

Interstellar Medium ◽

Spectral Type ◽

Column Density ◽

Resolving Power ◽

High Resolution Spectroscopy ◽

Luminosity Distance ◽

Ob Stars ◽

Dust Extinction ◽

Heating Source ◽

Dust Component

The precise characteristics of clouds and the nature of dust in the diffuse interstellar medium can only be extracted by inspecting the rare cases of single-cloud sightlines. In our nomenclature such objects are identified by interstellar lines, such as K I, that show at a resolving power of λ∕Δλ ~ 75 000 one dominating Doppler component that accounts for more than half of the observed column density. We searched for such sightlines using high-resolution spectroscopy towards reddened OB stars for which far-UV extinction curves are known. We compiled a sample of 186 spectra, 100 of which were obtained specifically for this project with UVES. In our sample we identified 65 single-cloud sightlines, about half of which were previously unknown. We used the CH/CH+ line ratio of our targets to establish whether the sightlines are dominated by warm or cold clouds. We found that CN is detected in all cold (CH/CH+ > 1) clouds, but is frequently absent in warm clouds. We inspected the WISE (3−22 μm) observed emission morphology around our sightlines and excluded a circumstellar nature for the observed dust extinction. We found that most sightlines are dominated by cold clouds that are located far away from the heating source. For 132 stars, we derived the spectral type and the associated spectral type-luminosity distance. We also applied the interstellar Ca II distance scale, and compared these two distance estimates with Gaia parallaxes. These distance estimates scatter by ~40%. By comparing spectral type-luminosity distances with those of Gaia, we detected a hidden dust component that amounts to a few mag of extinction for eight sightlines. This dark dust is populated by ≳ 1 μm large grains and predominately appears in the field of the cold interstellar medium.

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GALACTIC CENTER MINISPIRAL: INTERACTION MODES OF NEUTRON STARS

Acta Polytechnica ◽

10.14311/ap.2015.55.0203 ◽

2015 ◽

Vol 55 (3) ◽

pp. 203-214 ◽

Cited By ~ 1

Author(s):

Michal Zajacek ◽

Vladimir Karas ◽

Devaky Kunneriath

Keyword(s):

Neutron Stars ◽

Gaseous Medium ◽

Galactic Center ◽

Large Fraction ◽

Galactic Nuclei ◽

Star Cluster ◽

Ob Stars ◽

Gravitational Influence ◽

Simulation Results

Streams of gas and dust in the inner parsec of the Galactic center form a distinct feature known as the Minispiral, which has been studied in radio waveband as well as in the infrared wavebands. A large fraction of the Minispiral gas is ionized by radiation of OB stars present in the Nuclear Star Cluster (NSC). Based on the inferred mass in the innermost parsec ( ~106 solar masses), over ~103–104 neutron stars should move in the sphere of gravitational influence of the SMBH. We estimate that a fraction of them propagate through the denser, ionized medium concentrated mainly along the three arms of the Minispiral. Based on the properties of the gaseous medium, we discuss different interaction regimes of magnetised neutron stars passing through this region. Moreover, we sketch expected observational effects of these regimes. The simulation results may be applied to other galactic nuclei hosting NSC, where the expected distribution of the interaction regimes is different across different galaxy types.

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Chemical Abundances of OB Stars with High Projected Rotational Velocities

The Astrophysical Journal ◽

10.1086/323795 ◽

2001 ◽

Vol 563 (1) ◽

pp. 325-333 ◽

Cited By ~ 35

Author(s):

Simone Daflon ◽

Katia Cunha ◽

Keith Butler ◽

Verne V. Smith

Keyword(s):

Chemical Abundances ◽

Ob Stars

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The Fraction of Runaway OB Stars in the SMC Field

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308015299 ◽

2007 ◽

Vol 3 (S246) ◽

pp. 63-64

Author(s):

J. B. Lamb ◽

M. S. Oey

Keyword(s):

Dynamical Evolution ◽

Significant Fraction ◽

Line Of Sight ◽

Ob Stars ◽

Cluster Evolution

AbstractThe fraction of field OB stars that originate from clusters can help probe the dynamical evolution of clusters. Field stars represent a significant fraction (20-30%) of the OB population in galaxies, and estimates for the fraction of field OB stars that are runaways range from the classical value of <10% (Blaauw 1961) to contemporary results suggesting >90% (de Wit et al. 2005). We obtained Magellan IMACS observations on the kinematics of field OB stars in the SMC to examine the line-of-sight velocities of this population. Using these observations, we will estimate the fraction of runaways to serve as a probe of cluster evolution.

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