Ib Supergiant Research Articles

Anatomy of Pulsar XTE J1829-098: Ultramassive SXFT with a Dominant Nondipolar Magnetic Field, or the Third Canonical HMXB Caught at the Bottom of the Corbet Gap?

The X-ray binary pulsar XTE J1829-098 has been observed at extremely low luminosities for its spin period of 7.8448 s. Although its distance is uncertain by a factor of 4, the lowest observed X-ray fluxes may not correspond to its minimal-accretion propeller state or to nonaccreting states occurring at even lower X-ray luminosities, in which case the source has been caught at the bottom of the Corbet gap. We analyze all proposed distances D to the binary and the lowest X-ray fluxes, and we find only two physically acceptable solutions: (a) For D = 4.5 kpc (if the companion is a main-sequence B0 star), the neutron star is canonical with mass 1.41 M ⊙, radius 10.1 km, and a purely dipolar magnetic field as indicated by a cyclotron absorption line detected at 15 keV. In this case, the source has been observed at the bottom of the Corbet gap, the third high-mass X-ray binary pulsar to be caught in this state after the “twins” 4U 0115+63 and V 0332+53 found by Tsygankov et al. (b) For D = 18 kpc (if the companion is a B0.5Ib supergiant), the neutron star is ultramassive with mass 2.62 M ⊙, radius 18.7 km, and a dominant nondipolar magnetic field B mul = 1.26 TG (versus a dipolar component of only B dip = 0.43 TG). In this case, the source has been observed in its propeller state.

A catalog of rotational and radial velocities for evolved stars

Rotational and radial velocities have been measured for 1589 evolved stars of spectral types F, G and K and luminosity classes IV, III, II and Ib, based on observations carried out with the CORAVEL spectrometers. The precision in radial velocity is better than 0.30 km/s per observation, whereas rotational velocity uncertainties are typically 1.0 km/s for subgiants and giants and 2.0 km/s for class II giants and Ib supergiants.

Optical Counterpart of the Ultraluminous X‐Ray Source IC 342 X‐1

We present Chandra and HST observations of the ultraluminous X-ray source (ULX) IC 342 X-1. The Chandra and HST images are aligned using two X-ray emitting foreground stars. The astrometry corrected position for X-1 is R.A. = 03h45m55.61s, Decl. = +68d04m55.3s (J2000) with an error circle of 0.2". One extended optical source is found in the error circle, which could be the optical counterpart of X-1. The source shows an extended feature in HST images at long wavelengths, which is likely to be a superposition of two point sources, although it is possible that the dimmer one could be a jet. Both sources are much redder than typical for ULX optical counterparts. The brighter one has an absolute magnitude M_V = -5.2 +/- 0.2 and (B-V)_0 = 0.66 +/- 0.13 and the dimmer star is not detected in B and has (B-V)_0 > 2.1. Their colors are consistent with an F8 to G0 Ib supergiant or a carbon star, respectively. However, it is likely that part or most of the optical emission may be due to X-rays reprocessed by the companion star or the accretion disk. The stellar neighborhood of IC 342 X-1 lacks O stars and has a minimum age of ~10 Myr. This excludes the possibility that the surrounding nebula is powered by an energetic explosion of a single massive star that formed a black hole. We suggest that the nebula is most likely powered by an outflow from the X-ray source.

The Nature of SN 1961V

The nature of SN 1961V has been uncertain. Its peculiar optical light curve and slow expansion velocity are similar to those of superoutbursts of luminous blue variables (LBVs), but its nonthermal radio spectral index and declining radio luminosity are consistent with decades-old supernovae (SNe). We have obtained Hubble Space Telescope STIS images and spectra of the stars in the vicinity of SN 1961V and find object 7 identified by Filippenko and coworkers to be closest to the optical and radio positions of SN 1961V. Object 7 is the only point source detected in our STIS spectra, and only its Hα emission is detected; it cannot be the SN or its remnant because of the absence of forbidden lines. While the Hα line profile of object 7 is remarkably similar to that of η Carinae, the blue color (similar to an A2 Ib supergiant) and lack of appreciable variability are unlike known postoutburst LBVs. We have also obtained Very Long Baseline Array observations of SN 1961V at 18 cm. The nondetection of SN 1961V places a lower limit on the size of the radio-emitting region, 7.6 mas or 0.34 pc, which implies an average expansion velocity in excess of 4400 km s-1, much higher than the optical expansion velocity measured in 1961. We conclude the following: (1) An SN occurred in the vicinity of SN 1961V a few decades ago. (2) If the SN 1961V light maximum originates from a giant eruption of a massive star, object 7 is the most probable candidate for the survivor, but its blue color and lack of significant variability are different from a postoutburst η Car. (3) The radio SN and object 7 could be physically associated with each other through a binary system. (4) Object 7 needs to be monitored to determine its nature and relationship to SN 1961V.

The Optical Counterpart of an Ultraluminous X‐Ray Source in NGC 5204

Ultraluminous X-ray (ULX) sources are extranuclear point sources in external galaxies with LX = 1039-1041 ergs s-1 and are among the most poorly understood X-ray sources. To help understand their nature, we are trying to identify their optical counterparts by combining images from the Hubble Space Telescope (HST) and the Chandra X-Ray Observatory. Here we report on the optical counterpart for the ULX in NGC 5204, which has average X-ray luminosity of ~3 × 1039 ergs s-1 and has varied by a factor of 50% over the last 10 years. A unique optical counterpart to this ULX is found by carefully comparing the Chandra ACIS images and HST WFPC2 and ACS/HRC images. The spectral energy distribution and the HST/STIS far-ultraviolet (FUV) spectrum of this object show that it is a B0 Ib supergiant star with peculiarities, including the N V λ1240 emission line, which is uncommon in B stellar spectra but has been predicted for X-ray-illuminated accretion disks and seen in some X-ray binaries. Study of its FUV spectrum leads to a binary model for this ULX in which the B0 Ib supergiant is overflowing its Roche lobe and accreting onto the compact primary, probably a black hole. This picture predicts an orbital period of ~10 days for different black hole masses, which can be tested by future observations.

A survey of blue – ${\rm H}\alpha$objects in the galaxy M 33

For the purposes of a search for SS 433 type ob- jects, LBV stars and hypergiants in M 33, we have carried out a photometry of blue stars in H images of this galaxy. From 2332 listed OB stars, we have isolated 549 objects, which have H excess over stars of the sameV magnitude. Among them 81 emission stars (s) have been selected. About 60% of isolated objects found to be extended in H, among them 154 diuse (d) and 180 bubble{type (b) nebulae. 117 objects are compact (c) and faint H sources. These groups are dierent in colour indices, H fluxes, sur- face brightness and sizes. The most probable size of the H nebulae is FWHM =1 0 14 pc. There is evidence that their properties and location in the galaxy are dened by interstellar gas pressure and related to spiral arms. The do bjects are H II regions with an embedded star. The b objects are probably envelopes around WR stars or SN remnants. Among s{type objects we isolated a group of 20 brightest stars, which in their average properties t well to the parameters of blue hypergiants or LBV{type stars. The stars of intermediate brightness follow very well to blue Ia supergiants. The interstellar absorption derived from brightest H stars is AV =0 : 93 0: m 05. We classify the faintest stars as blue Ib supergiants, their average ab- sorption is AV 0: m 6. They are restricted in number by

A catalog of rotational and radial velocities for evolved stars

Rotational and radial velocities have been mea- sured for about 2000 evolved stars of luminosity classes IV, III, II and Ib covering the spectral region F, G and K. The survey was carried out with the CORAVEL spec- trometer. The precision for the radial velocities is better than 0.30 km s 1 , whereas for the rotational velocity mea- surements the uncertainties are typically 1.0 km s 1 for subgiants and giants and 2.0 km s 1 for class II giants and Ib supergiants. These data will add constraints to studies of the rotational behaviour of evolved stars as well as solid informations concerning the presence of external rotational brakes, tidal interactions in evolved binary sys- tems and on the link between rotation, chemical abun- dance and stellar activity. In this paper we present the rotational velocity v sini and the mean radial velocity for the stars of luminosity classes IV, III and II.

HD 105262, A NEWLY-DISCOVERED HR 4049 STAR WITH A LARGE PROPER MOTION

ABSTRACT HD 105262 has a spectrum like that of HR 4049 in having Balmer liens as in a Ib supergiant but very weak lines due to He I, Ca II, Si II, Ti II, fe I, Fe II, and Mg II. It has a published proper motion of 0.057" ± 0.011" yr-1. If the star had the luminosity of a Ib supergiant, its space motion would be several times the escape velocity from the Galaxy. HD 105262 does not have the spectral appearance of a horizontal-branch or post AGB star. The most likely explanation for the spectrum is the model proposed for HR 4049 by Lamers et al. (1986), Waelkens et al. (1987), and Lambert et al. (1988), namely a low-mass proto-planetary nebula star in which the narrow Balmer lines are formed in an extended atmosphere.

An analysis of the photospheric line profiles in F, G, and K supergiants

view Abstract Citations (53) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An Analysis of the Photospheric Line Profiles in F, G, and K Supergiants Gray, David F. ; Toner, C. G. Abstract The spectral-line broadening for 30 F, G, and K Ib supergiants has been measured. Fourier analysis for macroturbulence and rotation shows (1) macroturbulent velocities larger than but compatible with values found for lower luminosity stars and (2) rotation results that cannot be fully explained. Three plausible scenarios are suggested, but the one in which angular momentum of the surface 'shell' is conserved during the evolutionary changes experienced by these stars is favored. The unusual distribution of rotation velocities may result from a preferential alignment of rotation axes with the galactic poles. Publication: The Astrophysical Journal Pub Date: November 1987 DOI: 10.1086/165734 Bibcode: 1987ApJ...322..360G Keywords: F Stars; G Stars; K Stars; Line Shape; Photosphere; Supergiant Stars; Atmospheric Turbulence; Fourier Analysis; Spectral Line Width; Stellar Luminosity; Stellar Rotation; Stellar Spectrophotometry; Astrophysics; LINE PROFILES; STARS: ROTATION; STARS: SUPERGIANTS; TURBULENCE full text sources ADS | data products SIMBAD (28)

THE REMARKABLE SPECTRAL LINE ASYMMETRIES OF F AND G IB SUPERGIANT STARS.

ABSTRACT The authors observed a group of supergiants spanning the F5 Ib to K2 Ib interval. The line asymmetries of the F supergiants are found to be large and opposite in direction from the normal case seen in cooler and less-luminous stars, and in the Sun. There is a continuous and monotonic change in the bisector behavior with spectral type, with the transition from the anomalous to the normal asymmetry occurring near G1 Ib. The authors reproduce the observations with numerical simulations based on a simple two-stream model, and from this deduce velocities of rise of the hot material to be ≡ -25 km s-1 for the F Ib supergiants.

UVBY BETA PHOTOMETRY OF THE OPEN CLUSTER M 52.

ABSTRACT Photometric uvbyβ observations of the open cluster M52 (NGC 7654) are used to determine the cluster's distance modulus (V0 - Mυ = 10.83 ± 0.24) and mean cluster reddening (E(B - V) = 0.57). The likelihood of cluster membership of the F7 Ib supergiant 60°2532 is verified on evolutionary grounds; its absolute magnitude is determined to be Mυ = -4.42 ± 0.46. The cluster M52 is shown to be similar in age to the Pleiades and the α Persei cluster.

Multislit photoelectric magnetometer observations of Cepheids and supergiants - Probable detections of weak magnetic fields

We have assembled an instrument that measures the circular polarization in 230 spectral lines simultaneously. The instrument is capable of measuring longitudinal magnetic fields in bright stars with standard deviations of the order of 1 gauss. We have obtained several detections at the 2, 3, and up to 4.6 standard deviations level in the Cepheid variables ..cap alpha.. UMi and delta Cep and in the F8 Ib supergiant ..gamma.. Cyg, indicating longitudinal fields from 10 to 30 gauss. A thorough error analysis shows that we did not underestimate our errors and that the detections are very likely to be real. Other Cepheids observed with lower precision (sigmaapprox.40 gauss) do not give significant detections. It would thus appear that Cepheids as a class have magnetic fields with longitudinal components of a few tens of gauss. Our observations thus lend support to the hypothesis advanced by Stothers to reconcile pulsational and evolutionary masses. As a check on the technique, we have also observed the known magnetic star ..beta.. CrB, obtaining very high signal-to-noise ratio measurements that define a remarkably sinusoidal magnetic curve indicative of a dominate dipolar component.

HARVARD 20, A CLUSTER CONTAINING A YELLOW SUPERGIANT.

ABSTRACT UBV photometry and MK spectral types are presented for stars in the open cluster Harvard 20. Star counts are used to delineate the boundaries of this poorly-populated cluster (diameter = 9 arc min) and ZAMS fitting is used to derive a cluster distance of 1.75 ± 0.08 kpc. The evolutionary age of the cluster is estimated to be ̃6 (± 1) × 107 years, and a nonvariable G5 Ib supergiant, HDE 350801, is found to be a likely member. A comparison is made between Harvard 20 and other poor clusters of similar age which contain cepheid variables.

Stellar Atmospheres and Chemical Compositions of Galaxies

AbstractThe chemical compositions of external galaxies are usually found from their HII regions or composite absorption line spectra of their nuclei. In the Magellanic Clouds, however, individual stars are observable, but objects heretofore studied necessarily have been luminous la supergiants which border on the brink of instability. The image photon counting system on the Anglo-Australian Telescope makes it possible to observe fainter, more stable Ib supergiants. Energy distributions and Balmer line profiles for these stars can be fitted with theoretical predictions by Kurucz. A joint effort by J.E. Ross and B.J. O’Mara of the University of Queensland, Bruce Peterson of the Anglo-Australian Observatory, and a group at the University of California, Los Angeles to analyze three lb supergiants suggests that metals of the iron group are depleted by a factor of 2-3.5 with respect to the normal chemical composition of our own galaxy.

THE ULTRAVIOLET SPECTRUM OF LSI +61 303.

ABSTRACT IUE spectroscopy is presented of the radio variable emission-line star LSI +61°303, which may also be a source of X and γ rays. The UV continuum is complex and dues nut fit a single stellar model or power law. The UV flux and line spectrum suggest the primary is a mass-losing Ib supergiant but all possibilities involve some peculiarities compared with normal stars. The spectrum appears to contain a very strong, variable N III feature at λ1750.

Mass determination for the X-ray binary system Vela X-1

THE 6.9 mag B0.5 Ib supergiant HD77581 has been identified as the optical counterpart of the X-ray eclipsing binary system 3U0900–40 (Vela X-1)1,2, which eclipses with a period of 8.95 ± 0.02 d. The discovery of regular X-ray pulses in Vela X-l has also been reported3, with a mean pulse period of 282.9 s, modulated because of the radial velocity variation of the X-ray pulsar in its orbital motion. This makes Vela X-l the third X-ray binary system in which the orbits of both the optical and the X-ray component can be studied, and the following orbital parameters have been derived4, ex = 0.15±0.05, wx = 157° ± 24° and Kx = 268 ±12 km S−1. Analyses of the light curve of HD77581 have shown that the heating effect is too small to be detected2. Furthermore, the star is bright and the spectral lines are not very broad. This means that here the first relatively accurate direct mass determination of both the X-ray and the early-type supergiant components of an eclipsing X-ray binary becomes possible.

THE SPECTRUM OF FG SAGITTAE IN 1975.

ABSTRACT The spectmm of FG Sge in 1975 is compared with spectra of Ia and Ib supergiants of class F5 to G5. The cooling trend described by Langer, Kraft, and Anderson as taking place up to 1972 has continued, but possibly at a faster rate since 1972. The enhancement of rare-earth abundances also is confirmed. Molecular bands are not observed. Key words: spectral class - high-luminosity stars - abundances

The Atmospheres of the F-Type Supergiants II. The Line and Continuous Spectra

view Abstract Citations (39) References (46) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Atmospheres of the F-Type Supergiants II. The Line and Continuous Spectra Osmer, Patrick S. Abstract Coud spectra of 25 supergiants having spectral types from F2 to G5 and spectrophotometry of four F-type supergiants which are cluster members are used to determine their atmospheric characteristics. Curves of growth obtained from the spectra show that the micro turbulence determined from the Fe ii lines increases with luminosity and is correlated with the oxygen line strengths of Paper I. However, the Fe I microturbulence is insensitive to luminosity at spectral type F5. Both sets of lines have the same radial velocity in Ia and Ib supergiants of this type. Application of standard model-atmosphere techniques to the spectrophotometry produces reasonable effective temperatures, but the gravities of the class Ia supergiants are found to be a factor of 5 less than expected from stellar-interiors theory. The difference was less for the class Ib stars. Clearly, dynamical effects are important. Consideration of the effect of the turbulent motions on the pressure equilibrium indicates that the observed velocities are large enough to reduce the gas pressure and simulate a low gravity. The models also indicate that the observed microturbulence and a decrease in the continuous opacity account for the luminosity effect in the oxygen line. Although non-LTE effects may be present, they are not sensitive to luminosity. The gradient in radiation pressure beneath the photosphere exceeds the surface gravity in F-type supergiants with log g < 2. The resulting instability is the probable cause of mass motions in supergiants. This hypothesis is supported by the observations that the instability first occurs at the gravity where the oxygen line becomes sensitive to luminosity and the observed turbulence begins to increase. Finally, it is shown that a turbulent velocity which increases with height in the atmosphere can account for the different behavior of the Fe I and Fe ii lines at type F5 because the Fe I lines are formed at greater depths in the atmosphere. Publication: The Astrophysical Journal Supplement Series Pub Date: March 1972 DOI: 10.1086/190255 Bibcode: 1972ApJS...24..255O full text sources ADS | data products SIMBAD (26) Related Materials (1) Part 1: 1972ApJS...24..247O

A Search for Lithium and Beryllium in ib Supergiants and Cepheids

A Search for Lithium and Beryllium in ib Supergiants and Cepheids