1,150 research outputs found
Diagnostics Of Disks Around Hot Stars
We discuss three different observational diagnostics related to disks around hot stars: absorption line determinations of rotational velocities of Be stars; polarization diagnostics of circumstellar disks; and X-ray line diagnostics of one specific magnetized hot star, theta(1) Ori C. Some common themes that emerge from these studies include (a) the benefits of having a specific physical model as a framework for interpreting diagnostic data; (b) the importance of combining several different types of observational diagnostics of the same objects; and (c) that while there is often the need to reinterpret traditional diagnostics in light of new theoretical advances, there are many new and powerful diagnostics that are, or will soon be, available for the study of disks around hot stars
Recurrent shell infall events in a B0.5e star: HD 58978 1979-1988
Infall from the circumstellar envelope onto the bright B0.5 IVe star, HD 58978 was studied. The IUE data indicate that the star was surrounded by a low and moderately ionized circumstellar shell at least 12 times between 1979 and 1988. During 6 of these episodes, the signatures of cool circumstellar material were redshifted with respect to the photosphere by 20 to 80 km/sec. The data indicate that the transition from infall to minimal shell absorption can occur in under 10 days, and are consistent either with infall phases lasting up to 6 months, or with infall episodes shorter than 10 to 15 days. The long term behavior of the shell episodes is compared with variability in the stellar wind
Toward Mapping the Detailed Density Structure of Classical Be Circumstellar Disks
We present the preliminary results of near contemporaneous optical and infrared spectroscopic observations of select classical Be stars. We find strong evidence of oppositely oriented V/R hydrogen line profiles in the optical versus infrared spectra of zeta Tau, and briefly discuss how sustained contemporaneous optical and infrared spectroscopic observations might enable us to trace the detailed density structure of classical Be circumstellar disks
Properties of galactic B[e] supergiants: II. HDE 327083
The emission-line object HDE 327083 has long been considered to be one of the most luminous stars in the Milky Way. Nevertheless, no reliable physical parameters have been published for it. Our high-resolution optical spectroscopy revealed the presence of photospheric lines of a cool luminous companion. We detected significant antiphased radial velocity variations of the emission and absorption lines. The data obtained are still insufficient to derive a reliable orbital solution; however, the orbital period is most likely of the order of 6 months. We conclude that HDE 327083 is a binary system consisting of an early B-type primary and early F-type secondary, with luminosities log L/L⊙ = 5.0 ± 0.4 and 4.2 ± 0.4, respectively, and whose orbital plane is viewed nearly edge-on. We also obtained new multicolour optical and infrared photometry of HDE 327083. From both the photometric and spectroscopic data, we found that the system is located at a distance of 1.5 ± 0.5 kpc. Most of the circumstellar gas seems to be orbiting the primary and is distributed in a mildly flattened envelope with a height scale and velocity decreasing outward from the star. We suggest that HDE 327083 represents an advanced evolutionary stage of a β Lyrae type binary.Fil: Miroshnichenko, A. S.. Russian Academy of Sciences at Pulkovo; Rusia. University of Toledo; Estados UnidosFil: Levato, Orlando Hugo. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Bjorkman, K. S.. University of Toledo; Estados UnidosFil: Grosso, Monica Gladys. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; Argentin
Spectroscopy of B-type emission-line stars with compact dusty envelopes: HD 85567, Hen 3-140, and Hen 3-1398
We report the results of our spectroscopic observations (3600-5900 Ã…, R ≃ 16000 and 5750-8750 Ã…, R ≃ 11000) of three southern emission-line B-type stars associated with IRAS sources, HD 85567, Hen 3-140, and Hen 3-1398, whose nature and evolutionary state are not well-established yet. We also obtained new multicolour photometry of HD 85567 (UBV(RI)cJHKL) and (JHKLM). A large near-IR excess is found in Hen 3-140 for the first time. All three objects show double-peaked Fe II lines in emission. The Balmer emission lines are double-peaked in HD 85567 and Hen 3-140, while the He I lines are found in absorption. Hen 3-1398 displays triple-peaked Balmer lines as well as single-peaked He I and He II lines in emission. Fundamental parameters of the stars are estimated on the basis of both photometric and spectroscopic data. The whole set of their properties resemble that of a recently defined group of Be stars with warm dust (Sheikina et al. 2000).Fil: Miroshnichenko, A. S.. Russian Academy of Sciences at Pulkovo; Rusia. University Of Toledo (utoledo); Estados UnidosFil: Levato, Orlando Hugo. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Bjorkman, K. S.. University Of Toledo (utoledo); Estados UnidosFil: Grosso, Monica Gladys. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; Argentin
The continued optical to mid-IR evolution of V838 Monocerotis
The eruptive variable V838 Monocerotis gained notoriety in 2002 when it
brightened nine magnitudes in a series of three outbursts and then rapidly
evolved into an extremely cool supergiant. We present optical, near-IR, and
mid-IR spectroscopic and photometric observations of V838 Monocerotis obtained
between 2008 and 2012 at the Apache Point Observatory 3.5m, NASA IRTF 3m, and
Gemini South 8m telescopes. We contemporaneously analyze the optical & IR
spectroscopic properties of V838 Monocerotis to arrive at a revised spectral
type L3 supergiant and effective temperature Teff~2000--2200 K. Because there
are no existing optical observational data for L supergiants in the optical, we
speculate that V838 Monocerotis may represent the prototype for L supergiants
in this wavelength regime. We find a low level of Halpha emission present in
the system, consistent with interaction between V838 Monocerotis and its B3V
binary; however, we cannot rule out a stellar collision as the genesis event,
which could result in the observed Halpha activity. Based upon a two-component
blackbody fit to all wavelengths of our data, we conclude that, as of 2009, a
shell of ejecta surrounded V838 Monocerotis at a radius of R=263+/-10 AU with a
temperature of T=285+/-2 K. This result is consistent with IR interferometric
observations from the same era and predictions from the Lynch et al. model of
the expanding system, which provides a simple framework for understanding this
complicated system.Comment: 6 pages, 2 tables, 6 figures; accepted to A
Validity and Reliability of Electronic Devices to Measure Muscular Power during Linear Weight Lifting Movements
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Evolution of the Inner Circumstellar Envelope of V838 Monocerotis
We present imaging polarimetry observations of the eruptive variable V838
Monocerotis and its neighboring field obtained in 2002 October. The
polarization of field stars confirms the previously determined interstellar
polarization along the line of sight to V838 Mon. While V838 Mon showed
intrinsic polarization shortly after its second outburst on 2002 February 8,
all subsequent observations only showed a quiescent interstellar polarization
component. We find V838 Mon once again showed significant intrinsic
polarization in 2002 October, suggesting the presence of an asymmetrical
geometry of scattering material close to the star. Furthermore, an observed 90
degree position angle flip in the intrinsic polarization from 2002 February to
2002 October suggests that the distribution of nearby circumstellar material
has experienced significant changes. We discuss the opacity changes in the
evolving circumstellar cloud around V838 Mon that may explain these
observations.Comment: accepted by ApJL, 11 pages (including 2 figs, 2 tables
Probing the properties of Be star discs with spectroastrometry and NLTE radiative transfer modelling: beta CMi
While the presence of discs around classical Be stars is well established,
their origin is still uncertain. To understand what processes result in the
creation of these discs and how angular momentum is transported within them,
their physical properties must be constrained. This requires comparing high
spatial and spectral resolution data with detailed radiative transfer
modelling. We present a high spectral resolution, R~80,000, sub milli-arcsecond
precision, spectroastrometric study of the circumstellar disc around the Be
star beta CMi. The data are confronted with three-dimensional, NLTE radiative
transfer calculations to directly constrain the properties of the disc.
Furthermore, we compare the data to disc models featuring two velocity laws;
Keperian, the prediction of the viscous disc model, and angular momentum
conserving rotation. It is shown that the observations of beta CMi can only be
reproduced using Keplerian rotation. The agreement between the model and the
observed SED, polarisation and spectroastrometric signature of beta CMi
confirms that the discs around Be stars are well modelled as viscous decretion
discs.Comment: Accepted for publication in MNRA
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