Binarity in Cool Asymptotic Giant Branch Stars: A<i>GALEX</i>Search for Ultraviolet Excesses

Sahai, Raghvendra; Findeisen, K.; Paz, A. Gil de; Contreras, C. Sánchez

doi:10.1086/592559

Cited by 54 publications

(75 citation statements)

References 27 publications

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“…A star like V Hya would be a possible template (Sahai et al 2008). The above-mentioned GALEX flux is, however, a few orders of magnitude lower than what is expected for such an evolved star with an accretion disk.…”

Section: The Shape Of the Sedmentioning

confidence: 85%

Modelling the atmosphere of the carbon-rich Mira RU Virginis

Rau

Paladini

Hron

et al. 2015

A&A

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Context. We study the atmosphere of the carbon-rich Mira RU Vir using the mid-infrared high spatial resolution interferometric observations from VLTI/MIDI. Aims. The aim of this work is to analyse the atmosphere of the carbon-rich Mira RU Vir with hydrostatic and dynamic models, in this way deepening the knowledge of the dynamic processes at work in carbon-rich Miras. Methods. We compare spectro-photometric and interferometric measurements of this carbon-rich Mira AGB star with the predictions of different kinds of modelling approaches (hydrostatic model atmospheres plus MOD-More Of Dusty, self-consistent dynamic model atmospheres). A geometric model fitting tool is used for a first interpretation of the interferometric data. Results. The results show that a joint use of different kinds of observations (photometry, spectroscopy, interferometry) is essential for shedding light on the structure of the atmosphere of a carbon-rich Mira. The dynamic model atmospheres fit the ISO spectrum well in the wavelength range λ = [2.9, 25.0] µm. Nevertheless, a discrepancy is noticeable both in the SED (visible) and in the interferometric visibilities (shape and level), which is a possible explanation are intra-/inter-cycle variations in the dynamic model atmospheres, as well as in the observations. The presence of a companion star and/or a disk or a decrease in mass loss within the past few hundred years cannot be excluded, but these explanations are considered unlikely.

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Section: The Shape Of the Sedmentioning

confidence: 85%

Modelling the atmosphere of the carbon-rich Mira RU Virginis

Rau

Paladini

Hron

et al. 2015

A&A

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“…We indicate 1σ errors with dark shaded regions and indicate the locations of a few spectral features. Chemical subtype symbols that appear to the left of the object name are the same as in Figure 2. UV emission from AGB stars has been suggested as a potential tool to detect binary companions from AGB stars (Sahai et al 2008;Ortiz & Guerrero 2016). Over most of the electromagnetic spectrum luminous AGB stars will outshine main sequence and/or post-AGB companions.…”

Section: Scattering Of the Interstellar Radiation Fieldmentioning

confidence: 99%

A Catalog of GALEX Ultraviolet Emission from Asymptotic Giant Branch Stars

Montez

Ramstedt

Kastner

et al. 2017

ApJ

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We have performed a comprehensive study of the UV emission detected from AGB stars by the Galaxy Evolution Explorer (GALEX). Of the 468 AGB stars in our sample, 316 were observed by GALEX. In the NUV bandpass (λ eff ∼ 2310Å), 179 AGB stars were detected and 137 were not detected. Only 38 AGB stars were detected in the FUV bandpass (λ eff ∼ 1528Å). We find that NUV emission is correlated with optical to near infrared emission leading to higher detection fractions among the brightest, hence closest, AGB stars. Comparing the AGB time-variable visible phased light curves to corresponding GALEX NUV phased light curves we find evidence that for some AGB stars the NUV emission varies in phase with the visible light curves. We also find evidence that the NUV emission, and possibly, the FUV emission are anti-correlated with the circumstellar envelope density. These results suggest that the origin of the GALEX-detected UV emission is an inherent characteristic of the AGB stars that can most likely be traced to a combination of photospheric and chromospheric emission. In most cases, UV detections of AGB stars are not likely to be indicative of the presence of binary companions.

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“…To further examine the fields containing T Dra and R UMa, the available GALEX observations (Sahai et al 2008) were Notes.…”

Section: Data Description and Preparationmentioning

confidence: 99%

“…Montez et al 2010;Jeffries & Stevens 1996). Sahai et al (2008) searched for companions to AGB stars with GALEX UV observations in a sample of stars largely selected on the Hipparcos multiplicity flag. R UMa and T Dra were both found to have UV excesses.…”

Section: X-ray Emission From a Potential Companionmentioning

confidence: 99%

“…The completeness of the M-type (C/O < 1) sample has not been thoroughly investigated. To supplement the samples, we added nine stars found to have far-UV excess with GALEX (Sahai et al 2008) and 291 M-type Miras of Little-Marenin & Little (1990). Thirteen sample stars were found to have either serendipitous or targeted observations in the archives.…”

Section: Introductionmentioning

confidence: 99%

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Searching for X-ray emission from AGB stars

Ramstedt¹,

Montez²,

Kastner³

et al. 2012

A&A

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Context. Magnetic fields have been measured around asymptotic giant branch (AGB) stars of all chemical types using maser polarization observations. If present, a large-scale magnetic field would lead to X-ray emission, which should be observable using current X-ray observatories. Aims. The aim is to search the archival data for AGB stars that are intrinsic X-ray emitters. Methods. We have searched the ROSAT, CXO, and XMM-Newton archives for serendipitous X-ray observations of a sample of ∼500 AGB stars. We specifically searched for the AGB stars detected with GALEX. The data is calibrated, analyzed and the X-ray luminosities and temperatures are estimated as functions of the circumstellar absorption. Results. We identify 13 AGB stars as having either serendipitous or targeted observations in the X-ray data archives, however for a majority of the sources the detailed analysis show that the detections are questionable. Two new sources are detected by ROSAT: T Dra and R UMa. The spectral analysis suggests that the emission associated with these sources could be due to coronal activity or interaction across a binary system. Conclusions. Further observations of the detected sources are necessary to clearly determine the origin of the X-ray emission. Moreover, additional objects should be subject to targeted X-ray observations in order to achieve better constraints for the magnetic fields around AGB stars.

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Binarity in Cool Asymptotic Giant Branch Stars: AGALEXSearch for Ultraviolet Excesses

Cited by 54 publications

References 27 publications

Modelling the atmosphere of the carbon-rich Mira RU Virginis

Modelling the atmosphere of the carbon-rich Mira RU Virginis

A Catalog of GALEX Ultraviolet Emission from Asymptotic Giant Branch Stars

Searching for X-ray emission from AGB stars

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