Analysis of the recent long exposure Chandra X-ray observation of the early-type O star ζ Pup shows clear variability with a period previously reported in optical photometric studies. These 813 ks of ...HETGS observations taken over a roughly one-year time span have two signals of periodic variability: (1) a high-significance period of 1.7820 0.0008 day, and (2) a marginal detection of periodic behavior close to either 5 days or 6 days. A BRITE-Constellation nanosatellite optical photometric monitoring (using near-contemporaneous observations to the Chandra data) confirms a 1.78060 0.00088 day period for this star. The optical period coincides with the new Chandra period within their error ranges, demonstrating a link between these two wave bands and providing a powerful lever for probing the photosphere-wind connection in this star. The phase lag of the X-ray maximum relative to the optical maximum is ∼ φ = 0.45, but consideration of secondary maxima in both data sets indicates possibly two "hot" spots on the star with an X-ray phase lag of φ = 0.1 each. The details of this periodic variation of the X-rays are probed by displaying a phased and trailed X-ray spectrum and by constructing phased light curves for wavelength bands within the HETGS spectral coverage (ranging down to bands encompassing groups of emission lines). We propose that the 1.78 day period is the stellar rotation period and explore how stellar bright spots and associated corotating interaction regions (CIRs) could explain the modulation of this star's optical and X-ray output and their phase difference.
mu Columbae is a prototypical weak-wind O star for which we have obtained a high-resolution X-ray spectrum with the Chandra LETG/ACIS instrument and a low-resolution spectrum with Suzaku. This allows ...us, for the first time, to investigate the role of X-rays on the wind structure in a bona fide weak-wind system and to determine whether there actually is a massive hot wind. The X-ray emission measure indicates that the outflow is an order of magnitude greater than that derived from UV lines and is commensurate with the nominal wind-luminosity relationship for O stars. Therefore, the "weak-wind problem"-identified from cool wind UV/optical spectra-is largely resolved by accounting for the hot wind seen in X-rays. From X-ray line profiles, Doppler shifts, and relative strengths, we find that this weak-wind star is typical of other late O dwarfs. The X-ray spectra do not suggest a magnetically confined plasma-the spectrum is soft and lines are broadened; Suzaku spectra confirm the lack of emission above 2 keV. Nor do the relative line shifts and widths suggest any wind decoupling by ions. The He-like triplets indicate that the bulk of the X-ray emission is formed rather close to the star, within five stellar radii. Our results challenge the idea that some OB stars are "weak-wind" stars that deviate from the standard wind-luminosity relationship. The wind is not weak, but it is hot and its bulk is only detectable in X-rays.
Marked correlations are reported between the ionization of the X-ray line spectra of normal OB stars, as observed by the Chandra X-Ray Observatory, and their optical spectral types. These ...correlations include the progressive weakening of the higher ionization relative to the lower ionization X-ray lines with advancing spectral type, and the similarly decreasing intensity ratios of the H-like to He-like lines of the Delta *a ions. These relationships were not predicted by models, nor have they been clearly evident in astrophysical studies of a few objects; rather, they have emerged from morphological analysis of an adequate (albeit still small) sample, from which known peculiar objects such as magnetic stars and very rapid rotators have been isolated to reveal the normal trends. This process is analogous to that which first demonstrated the strong relationships between the UV wind profiles and the optical spectral types of normal OB stars, which likely bear a physical as well as a historical connection to the present X-ray results. Since the optical spectral types are calibrated in terms of fundamental stellar parameters, it follows that the winds and X-ray spectra are determined by the latter. These observations provide strong guidance for further astrophysical modeling of these phenomena.
The high-resolution X-ray spectroscopy made possible by the 1999 deployment of the Chandra X-ray Observatory has revolutionized our understanding of stellar X-ray emission. Many puzzles remain, ...however, particularly regarding the mechanisms of X-ray emission from OB stars. Although numerous Individual stars have been observed in high resolution, realizing the full scientific potential of these observations will necessitate studying the high-resolution Chandra data set as a whole. To facilitate the rapid comparison and characterization of stellar spectra, we have compiled a uniformly processed database of all stars observed with the Chandra High-Energy Transmission Grating (HETG). This database, known as X-Atlas, is accessible through a Web interface with searching, data retrieval, and interactive plotting capabilities. For each target, X-Atlas also features predictions of the low-resolution ACIS spectra convolved from the HETG data for comparison with stellar sources in archival ACIS images. Preliminary analyses of the hardness ratios, quantiles, and spectral fits derived from the predicted ACIS spectra reveal systematic differences between the high- and low-mass stars in the atlas and offer evidence for at least two distinct classes of high-mass stars. A high degree of X-ray variability is also seen in both high- and low-mass stars, including Capella, long thought to exhibit minimal variability. X-Atlas contains over 130 observations of approximately 25 high-mass stars and 40 low-mass stars and will be updated as additional stellar HETG observations become public. The atlas has recently expanded to nonstellar point sources, and Low-Energy Transmission Grating (LETG) observations are currently being added as well.
An Introduction to the Chandra Carina Complex Project Townsley, Leisa K; Broos, Patrick S; Corcoran, Michael F ...
The Astrophysical journal. Supplement series,
05/2011, Letnik:
194, Številka:
1
Journal Article, Web Resource
Recenzirano
Odprti dostop
The Great Nebula in Carina provides an exceptional view into the violent massive star formation and feedback that typifies giant H II regions and starburst galaxies. We have mapped the Carina ...star-forming complex in X-rays, using archival Chandra data and a mosaic of 20 new 60 ks pointings using the Chandra X-ray Observatory's Advanced CCD Imaging Spectrometer, as a testbed for understanding recent and ongoing star formation and to probe Carina's regions of bright diffuse X-ray emission. This study has yielded a catalog of properties of >14,000 X-ray point sources; >9800 of them have multiwavelength counterparts. Using Chandra's unsurpassed X-ray spatial resolution, we have separated these point sources from the extensive, spatially-complex diffuse emission that pervades the region; X-ray properties of this diffuse emission suggest that it traces feedback from Carina's massive stars. In this introductory paper, we motivate the survey design, describe the Chandra observations, and present some simple results, providing a foundation for the 15 papers that follow in this special issue and that present detailed catalogs, methods, and science results.
The low-resolution X-ray spectra around eta Car covering Trumpler 16 and part of Trumpler 14 have been extracted from a Chandra CCD ACIS image. Various analysis techniques have been applied to the ...spectra based on their count rates. The spectra with the greatest number of counts (HD 93162 = WR 25, HD 93129 AB, and HD 93250) have been fitted with a wind model, which uses several components with different temperatures and depths in the wind. Weaker spectra have been fitted with Raymond-Smith models. The weakest spectra are simply intercompared with strong spectra. In general, fits produce reasonable parameters based on knowledge of the extinction from optical studies and on the range of temperatures for high- and low-mass stars. Direct comparisons of spectra confirm the consistency of the fitting results and also hardness ratios for cases of unusually large extinction in the clusters. The spectra of the low- mass stars are harder than the more massive stars. Stars in the sequence evolving from the main sequence (HD 93250) through the system containing the O supergiant (HD 93129 AB) and then through the Wolf-Rayet stage (HD 93162), presumably ending in the extreme example of eta Car, share the property of being unusually luminous and hard in X-rays. For these X-ray-luminous stars, their high mass and evolutionary status (from the very last stages of the main sequence and beyond) is the common feature. Their binary status is mixed, and their magnetic status is still uncertain.
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