Physical Sciences and Mathematics Commons^™

Variability In X-Ray Line Ratios In Helium-Like Ions Of Massive Stars: The Wind-Driven Case, Richard Ignace, Z. Damrau, K. T. Hole

ETSU Faculty Works

Context. High spectral resolution and long exposure times are providing unprecedented levels of data quality of massive stars at X-ray wavelengths.

Aims. A key diagnostic of the X-ray emitting plasma are the fir lines for He-like triplets. In particular, owing to radiative pumping effects, the forbidden-to-intercombination line luminosity ratio, R = f∕i, can be used to determine the proximity of the hot plasma to the UV-bright photospheres of massive stars. Moreover, the era of large observing programs additionally allows for investigation of line variability.

Methods. This contribution is the second to explore how variability in the line …

Coordinated Uv And X-Ray Spectroscopic Observations Of The O-Type Giant Ξ Per: The Connection Between X-Rays And Large-Scale Wind Structure, Derek Massa, Lidi Oskinova, Raman Prinja, Richard Ignace

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We present new, contemporaneous Hubble Space Telescope STIS and XMM-Newton observations of the O7 III(n)((f)) star ξ Per. We supplement the new data with archival IUE spectra, to analyze the variability of the wind lines and X-ray flux of ξ Per. The variable wind of this star is known to have a 2.086-day periodicity. We use a simple, heuristic spot model that fits the low-velocity (near-surface) IUE wind line variability very well, to demonstrate that the low-velocity absorption in the new STIS spectra of N iv λ1718 and Si iv λ1402 vary with the same 2.086-day period. It …

The Polarization Mode Of The Auroral Radio Emission From The Early-Type Star Hd 142301, P. Leto, C. Trigilio, Lidi M. Oskinova, Richard Ignace, C. S. Buemi, G. Umana, F. Cavallaro, A. Ingallinera, F. Bufano, N. M. Phillips, C. Agliozzo, L. Cerrigone, H. Todt, S. Riggi, F. Leone

ETSU Faculty Works

We report the detection of the auroral radio emission from the early-type magnetic star HD 142301. New VLA observations of HD 142301 detected highly polarized amplified emission occurring at fixed stellar orientations. The coherent emission mechanism responsible for the stellar auroral radio emission amplifies the radiation within a narrow beam, making the star where this phenomenon occurs similar to a radio lighthouse. The elementary emission process responsible for the auroral radiation mainly amplifies one of the two magneto-ionic modes of the electromagnetic wave. This explains why the auroral pulses are highly circularly polarized. The auroral radio emission of HD 142301 …

Asymmetric Shapes Of Radio Recombination Lines From Ionized Stellar Winds, Richard Ignace

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Recombination line profile shapes are derived for ionized spherical stellar winds at radio wavelengths. It is assumed that the wind is optically thick owing to free-free opacity. Emission lines of arbitrary optical depth are obtained assuming that the free-free photosphere forms in the outer, constant expansion portion of the wind. Previous works have derived analytic results for isothermal winds when the line and continuum source functions are equal. Here, semi-analytic results are derived for unequal source functions to reveal that line shapes can be asymmetric about line center. A parameter study is presented and applications discussed.

On The Apparent Absence Of Wolf–Rayet+Neutron Star Systems: The Curious Case Of Wr124, Jesus A. Toala, Lidi Oskinova, W.R. Hamann, Richard Ignace, A.A. C. Sander, H. Todt, Y.H. Chu, M. A. Guerrero, R. Hainich, R. Hainich, J. M. Terrejon

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Among the different types of massive stars in advanced evolutionary stages is the enigmatic WN8h type. There are only a few Wolf–Rayet (WR) stars with this spectral type in our Galaxy. It has long been suggested that WN8h-type stars are the products of binary evolution that may harbor neutron stars (NS). One of the most intriguing WN8h stars is the runaway WR 124 surrounded by its magnificent nebula M1-67. We test the presence of an accreting NS companion in WR 124 using ~100 ks long observations by the Chandra X-ray observatory. The hard X-ray emission from WR 124 with a …

Probing The Rotational Velocity Of Galactic Wo Stars With Spectropolarimetry, H. F. Stevance, Richard Igance, P. A. Crowther, J. R. Maund, B. Davies, G. Rate

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Oxygen sequence Wolf-Rayet stars (WO) are thought to be the final evolution phase of some high-mass stars, as such they may be the progenitors of Type Ic SNe as well as potential progenitors of broad-lined Ic and long gamma-ray bursts. We present the first spectropolarimetric observations of the Galactic WO stars WR93b and WR102 obtained with FORS1 on the Very Large Telescope. We find no sign of a line effect, which could be expected if these stars were rapid rotators. We also place constraints on the amplitude of a potentially undetected line effect. This allows us to derive upper limits …

A Study Of Hα Line Profile Variations In Β Lyr, Richard Ignace, Sharon K. Gray, Macno A. Magno, Gary D. Henson, Derek Massa

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We examine over 160 archival Hα spectra from the Ritter Observatory for the interacting binary β Lyr obtained between 1996 and 2000. The emission is characteristically double-peaked, but asymmetric, and with an absorption feature that is persistently blueshifted. Using a set of simplifying assumptions, phase varying emission line profiles are calculated for Hα formed entirely in a Keplerian disk, and separately for the line formed entirely from an off-center bipolar flow. However, a dynamic spectrum of the data indicates that the blueshifted feature is not always present, and the data are even suggestive of a drift of the …

An X-Ray Study Of Two B+B Binaries: Ah Cep And Cw Cep, Richard Ignace, K. T. Hole, Lidia M. Oskinova, J. P. Rotter

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AH Cep and CW Cep are both early B-type binaries with short orbital periods of 1.8 days and 2.7 days, respectively. All four components are B0.5V types. The binaries are also double-lined spectroscopic and eclipsing. Consequently, solutions for orbital and stellar parameters make the pair of binaries ideal targets for a study of the colliding winds between two B stars. Chandra ACIS-I observations were obtained to determine X-ray luminosities. AH Cep was detected with an unabsorbed X-ray luminosity at a 90% confidence interval of erg s−1, or , relative to the combined Bolometric luminosities of the two components. While formally …

Limb Darkening And Planetary Transits: Testing Center-To-Limb Intensity Variations And Limb-Darkening Directly From Model Stellar Atmospheres, Hilding R. Neilson, Joseph T. Mcneil, Richard Ignace, John B. Lester

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The transit method, employed by Microvariability and Oscillation of Stars (MOST), Kepler, and various ground-based surveys has enabled the characterization of extrasolar planets to unprecedented precision. These results are precise enough to begin to measure planet atmosphere composition, planetary oblateness, starspots, and other phenomena at the level of a few hundred parts per million. However, these results depend on our understanding of stellar limb darkening, that is, the intensity distribution across the stellar disk that is sequentially blocked as the planet transits. Typically, stellar limb darkening is assumed to be a simple parameterization with two coefficients that are derived …

On The Binary Nature Of Massive Blue Hypergiants: High-Resolution X-Ray Spectroscopy Suggests That Cyg Ob2 12 Is A Colliding Wind Binary - Iopscience, Lidia M. Oskinova, David P. Huenemoerder, Wolf-Rainer Hamann, Tomer Shenar, A. A.C. Sander, Richard Ignace, H. Todt, R. Hainich

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The blue hypergiant Cyg OB2 12 (B3Ia+) is a representative member of the class of very massive stars in a poorly understood evolutionary stage. We obtained its high-resolution X-ray spectrum using the Chandra observatory. PoWR model atmospheres were calculated to provide realistic wind opacities and to establish the wind density structure. We find that collisional de-excitation is the dominant mechanism depopulating the metastable upper levels of the forbidden lines of the He-like ions Si xivand Mg xii. Comparison between the model and observations reveals that X-ray emission is produced in a dense plasma, which could reside only at the photosphere …

Revealing The Structure Of The Outer Disks Of Be Stars, Robert Klement, Anthony C. Carciofi, Thomas Rivinius, Lynn D. Matthews, Rodrigo G. Vieira, Richard Ignace, Jon E. Bjorkman, B. C. Mota, Daniel M. Faes, A. D. Bratcher, M. Cure, Stanislav Stefl

ETSU Faculty Works

Context. The structure of the inner parts of Be star disks (≲ 20 stellar radii) is well explained by the viscous decretion disk (VDD) model, which is able to reproduce the observable properties of most of the objects studied so far. The outer parts, on the other hand, are not observationally well-explored, as they are observable only at radio wavelengths. A steepening of the spectral slope somewhere between infrared and radio wavelengths was reported for several Be stars that were previously detected in the radio, but a convincing physical explanation for this trend has not yet been provided.

Aims. We …

On The Absence Of Non-Thermal X-Ray Emission Around Runaway O Stars, Jesus A. Toalá, Lidia M. Oskinova, Richard Ignace

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Theoretical models predict that the compressed interstellar medium around runaway O stars can produce high-energy non-thermal diffuse emission, in particular, non-thermal X-ray and γ-ray emission. So far, detection of non-thermal X-ray emission was claimed for only one runaway star, AE Aur. We present a search for non-thermal diffuse X-ray emission from bow shocks using archived XMM-Newton observations for a clean sample of six well-determined runaway O stars. We find that none of these objects present diffuse X-ray emission associated with their bow shocks, similarly to previous X-ray studies toward ζ Oph and BD+43°3654. We carefully investigated multi-wavelength observations of …

"Blinded By The Lines: Mid-Ir Spectra Of Mira Variables Taken With Spitzer", Dana Baylis-Aguirre, Michelle J. Creech-Eakman, Donald G. Luttermoser, Tina Gueth

ETSU Faculty Works

We present preliminary analysis of mid-infrared spectra of M-type and C-type Mira variables. Due to the brightness of this sample, it is straightforward to monitor changes with phase in the infrared spectral features of these regular pulsators. We have spectra of 25 Mira variables, taken with phase, using the Spitzer Infrared Spectrograph (IRS) high-resolution module. Each star has multiple spectra obtained over a one-year period from 2008-09. This is a rich, unique data set due to multiple observations of each star and the high signal-to-noise ratio from quick exposure times to prevent saturation of the IRS instrument. This paper focuses …

Modeling X-Ray Emission Line Profiles From Massive Star Winds - A Review, Richard Igance

ETSU Faculty Works

The Chandra and XMM-Newton X-ray telescopes have led to numerous advances in the study and understanding of astrophysical X-ray sources. Particularly important has been the much increased spectral resolution of modern X-ray instrumentation. Wind-broadened emission lines have been spectroscopically resolved for many massive stars. This contribution reviews approaches to the modeling of X-ray emission line profile shapes from single stars, including smooth winds, winds with clumping, optically thin versus thick lines, and the effect of a radius-dependent photoabsorption coefficient.

X-Ray Observations Of Bow Shocks Around Runaway O Stars. The Case Of Ζ Oph And Bd+43°3654, Jesus Toala, Lidia M. Oskinova, A. González-Galán, M. A. Guerrero, Richard Ignace, M. Pohl

ETSU Faculty Works

Non-thermal radiation has been predicted within bow shocks around runaway stars by recent theoretical works. We present X-ray observations toward the runaway stars ζ Oph by Chandra and Suzaku and of BD+43°3654 by XMM-Newton to search for the presence of non-thermal X-ray emission. We found no evidence of non-thermal emission spatially coincident with the bow shocks; nonetheless, diffuse emission was detected in the vicinity of ζ Oph. After a careful analysis of its spectral characteristics, we conclude that this emission has a thermal nature with a plasma temperature of T ≈ 2 × 106 K. The cometary shape of this …

The Mimes Survey Of Magnetism In Massive Stars: Introduction And Overview, G. A. Wade, C. Neiner, E. Alecian, H. H. Grunhunt, V. Petit, B. Batz, D. A. Bohlender, D. H. Cohen, H. F. Henrichs, O. Kochukhov, J. D. Landstreet, N. Manset, F. Martins, S. Mathis, M. E. Oksala, S. P. Owocki, Th. Rivinius, M. E. Schultz, J. O. Sundqvist, R. H.D. Townsend, A. Doula, J. C. Bouret, J. Braithwaite, M. Briquet, A. C. Carciofi, A. David-Uraz, C. P. Folsom, A. W. Fullerton, B. Leroy, W. L.F. Marcolino, A. F.J. Moffat, Y. Naze, N. St Louis, M. Auriere, S. Bagnulo, J. D. Bailey, R. H. Barba, A. Blazere, T. Bohm, C. Catala, J-F Donati, L. Ferrario, D. Harrington, I. D. Howarth, Richard Ignace, L. Kaper, T. Luftinger, R. Prinja, J. S. Vink, W. W. Weiss, I. Yakunin

ETSU Faculty Works

The MiMeS (Magnetism in Massive Stars) project is a large-scale, high-resolution, sensitive spectropolarimetric investigation of the magnetic properties of O- and early B-type stars. Initiated in 2008 and completed in 2013, the project was supported by three Large Program allocations, as well as various programmes initiated by independent principal investigators, and archival resources. Ultimately, over 4800 circularly polarized spectra of 560 O and B stars were collected with the instruments ESPaDOnS (Echelle SpectroPolarimetric Device for the Observation of Stars) at the Canada–France–Hawaii Telescope, Narval at the Télescope Bernard Lyot and HARPSpol at the European Southern Observatory La Silla 3.6 m …

Period Change And Stellar Evolution Of Β Cephei Stars, Hilding R. Neilson, Richard Ignace

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The β Cephei stars represent an important class of massive star pulsators that probe the evolution of B-type stars and the transition from main sequence to hydrogen-shell burning evolution. By understanding β Cep stars, we gain insights into the detailed physics of massive star evolution, including rotational mixing, convective core overshooting, magnetic fields, and stellar winds, all of which play important roles. Similarly, modeling their pulsation provides additional information into their interior structures. Furthermore, measurements of the rate of change of pulsation period offer a direct measure of β Cephei stellar evolution. In this work, we compute state-of-the-art stellar evolution …

The Strange Evolution Of The Large Magellanic Cloud Cepheid Ogle-Lmc-Cep1812, Hilding R. Neilson, Robert G. Izzard, Nobert Langer, Richard Ignace

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Classical Cepheids are key probes of both stellar astrophysics and cosmology as standard candles and pulsating variable stars. It is important to understand Cepheids in unprecedented detail in preparation for upcoming Gaia, James Webb Space Telescope (JWST) and extremely-large telescope observations. Cepheid eclipsing binary stars are ideal tools for achieving this goal, however there are currently only three known systems. One of those systems, OGLE-LMC-CEP1812, raises new questions about the evolution of classical Cepheids because of an apparent age discrepancy between the Cepheid and its red giant companion. We show that the Cepheid component is actually the product of a …

A Coordinated X-Ray And Optical Campaign Of The Nearest Massive Eclipsing Binary, Δ Orionis Aa: Ii. X-Ray Variability., Joy Nichols, D. Huenemoerder, Michael Corcoran, W. Waldron, Y. Nazé, Andy Pollock, A. Moffat, J. Lauer, Tomer Shenar, C. Russell, N. Richardson, H. Pablo, N. Evans, K. Hamaguchi, T. Gull, W.-R. Hamann, L. Oskinova, Richard Ignace, Jennifer Hoffman, K. Hole, Jamie Lomax

ETSU Faculty Works

We present time-resolved and phase-resolved variability studies of an extensive X-ray high-resolution spectral data set of the δ Ori Aa binary system. The four observations, obtained with Chandra ACIS HETGS, have a total exposure time of ≈ 479 ks and provide nearly complete binary phase coverage. Variability of the total X-ray flux in the range of 5–25 Å is confirmed, with a maximum amplitude of about ±15% within a single ≈ 125 ks observation. Periods of 4.76 and 2.04 days are found in the total X-ray flux, as well as an apparent overall increase in the flux level throughout the …

A Coordinated X-Ray And Optical Campaign Of The Nearest Massive Eclipsing Binary, Δ Orionis Aa. Iii. Analysis Of Optical Photometric (Most) And Spectroscopic (Ground Based) Variations., Herbert Pablo, Noel Richardson, Anthony Moffat, Michael Corcoran, Tomer Shenar, Omar Benvenuto, Jim Fuller, Yaël Nazé, Jennifer Hoffman, Anatoly Miroshnichenko, Jesús Apellániz, Nancy Evans, Thomas Eversberg, Ken Gayley, Ted Gull, Kenji Hamaguchi, Wolf-Rainer Hamann, Huib Henrichs, Tabetha Hole, Richard Ignace, Rosina Iping, Jennifer Lauer, Maurice Leutenegger, Jamie Lomax, Joy Nichols, Lida Oskinova, Stan Owocki, Andy Pollock, Christopher Russell, Wayne Waldron, Christian Buil, Thierry Garrel, Keith Graham, Bernard Heathcote, Thierry Lemoult, Dong Li, Benjamin Mauclaire, Mike Potter, Jose Ribeiro, Jaymie Matthews, Chris Cameron, David Guenther, Rainer Kuschnig, Jason Rowe, Slavek Rucinski, Dimitar Sasselov, Werner Weiss

ETSU Faculty Works

We report on both high-precision photometry from the Microvariability and Oscillations of Stars (MOST) space telescope and ground-based spectroscopy of the triple system δ Ori A, consisting of a binary O9.5II+early-B(Aa1 and Aa2) with P=5.7 days, and a more distant tertiary(O9 IV P 400 years). This data was collected in concert with X-ray spectroscopy from the Chandra X-ray Observatory. Thanks to continuous coverage for three weeks, the MOST light curve reveals clear eclipses between Aa1 and Aa2 for the first time in non-phased data. From the spectroscopy, we have a well-constrained radial velocity (RV)curve of Aa1. While we are unable …

A Coordinated X-Ray And Optical Campaign Of The Nearest Massive Eclipsing Binary, Δ Ori Aa: I. Overview Of The X-Ray Spectrum., Michael Corcoran, Joy Nichols, H. Pablo, Tomer Shenar, Andy Pollock, W. Waldron, A. Moffat, N. Richardson, C. Russell, K. Hamaguchi, D. Huenemoerder, L. Oskinova, W.-R. Hamann, Y. Nazé, Richard Ignace, Nancy Evans, Jamie Lomax, J. Hoffman, K. Gayley, S. Owocki, M. Leutenegger, T. Gull, K. Hole, J. Lauer, R. Iping

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We present an overview of four deep phase-constrained Chandra HETGS X-ray observations of δ Ori A. Delta Ori A is actually a triple system that includes the nearest massive eclipsing spectroscopic binary, δ Ori Aa, the only such object that can be observed with little phase-smearing with the Chandra gratings. Since the fainter star, δ Ori Aa2, has a much lower X-ray luminosity than the brighter primary (δ Ori Aa1), δ Ori Aa provides a unique system with which to test the spatial distribution of the X-ray emitting gas around δ Ori Aa1 via occultation by the photosphere of, and …

Probing Wolf–Rayet Winds: Chandra/Hetg X-Ray Spectra Of Wr 6, David P. Huenemoerder, K. G. Gayley, Wolf-Rainer Hamann, Richard Ignace, J. S. Nichols, Lidia M. Oskinova, A. M.T. Pollock, Nobert S. Schulz, Tomer Shenar

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With a deep Chandra/HETGS exposure of WR 6, we have resolved emission lines whose profiles show that the X-rays originate from a uniformly expanding spherical wind of high X-ray-continuum optical depth. The presence of strong helium-like forbidden lines places the source of X-ray emission at tens to hundreds of stellar radii from the photosphere. Variability was present in X-rays and simultaneous optical photometry, but neither were correlated with the known period of the system or with each other. An enhanced abundance of sodium revealed nuclear-processed material, a quantity related to the evolutionary state of the star. The characterization of …

Polarimetric Modeling Of Corotating Interaction Regions (Cirs) Threading Massive-Star Winds., Richard Ignace, Nicole St-Louis, Felix Proulx-Giraldeau

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Massive star winds are complex radiation-hydrodynamic (sometimes magnetohydrodynamic) outflows that are propelled by their enormously strong luminosities. The winds are often found to be structured and variable, but can also display periodic or quasi-periodic behavior in a variety of wind diagnostics. The regular variations observed in putatively single stars, especially in UV wind lines, have often been attributed to corotating interaction regions (CIRs) like those seen in the solar wind. We present light curves for variable polarization from winds with CIR structures. We develop a model for a time-independent CIR based on a kinematical description. Assuming optically thin electron scattering, …

New Multiwavelength Observations Of The Of?P Star Cpd -28◦ 2561., S. Hubrig, M. Schöller, A. Kholtygin, H. Tsumura, A. Hoshino, S. Kitamoto, L. Oskinova, Richard Ignace, H. Todt, I. Ilyin

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A rather strong mean longitudinal magnetic field of the order of a few hundred gauss was detected a few years ago in the Of?p star CPD −28° 2561 using FORS2 (FOcal Reducer low dispersion Spectrograph 2) low-resolution spectropolarimetric observations. In this work, we present additional low-resolution spectropolarimetric observations obtained during several weeks in 2013 December using FORS 2 mounted at the 8-m Antu telescope of the Very Large Telescope (VLT). These observations cover a little less than half of the stellar rotation period of 73.41 d mentioned in the literature. The behaviour of the mean longitudinal magnetic field is consistent …

On X-Ray Pulsations In Beta Cephei-Type Variables, L. Oskinova, H. Todt, D. Huenemoerder, S. Hubrig, Richard Ignace, W.-R. Hamann, L. Balona

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Beta Cephei-type variables are early B-type stars that are characterized by oscillations observable in their optical light curves. At least one Beta Cep-variable also shows periodic variability in X-rays. Here we study the X-ray light curves in a sample of beta Cep-variables to investigate how common X-ray pulsations are for this type of stars. We searched the Chandra and XMM-Newton X-ray archives and selected stars that were observed by these telescopes for at least three optical pulsational periods. We retrieved and analyzed the X-ray data for kappa Sco, beta Cru, and alpha Vir. The X-ray light curves of these objects …

Evidence Of A Mira-Like Tail And Bow Shock About The Semi-Regular Variable V Cvn From Four Decades Of Polarization Measurements., Hilding Neilson, Richard Ignace, Beverly Smith, Gary Henson, Alyssa Adams

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Polarization is a powerful tool for understanding stellar atmospheres and circumstellar environments. Mira and semi-regular variable stars have been observed for decades and some are known to be polarimetrically variable, however, the semi-regular variable V Canes Venatici displays an unusually large, unexplained amount of polarization. We present ten years of optical polarization observations obtained with the HPOL instrument, supplemented by published observations spanning a total interval of about forty years for V CVn. We find that V CVn shows large polarization variations ranging from 1 - 6%. We also find that for the past forty years the position angle measured …

Discovery Of X-Ray Pulsations From A Massive Star., Lidia Oskinova, Yael Nazé, Helge Todt, David Huenemoerder, Richard Ignace, Swetlana Hubrig, Wolf-Rainer Hamann

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X-ray emission from stars much more massive than the Sun was discovered only 35 years ago. Such stars drive fast stellar winds where shocks can develop, and it is commonly assumed that the X-rays emerge from the shock-heated plasma. Many massive stars additionally pulsate. However, hitherto it was neither theoretically predicted nor observed that these pulsations would affect their X-ray emission. All X-ray pulsars known so far are associated with degenerate objects, either neutron stars or white dwarfs. Here we report the discovery of pulsating X-rays from a non-degenerate object, the massive B-type star ξ1 CMa. This star is a …

Faraday Rotation Effects For Diagnosing Magnetism In Bubble Environments., Richard Ignace

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Faraday rotation is a process by which the position angle (PA) of background linearly polarized light is rotated when passing through an ionized and magnetized medium. The effect is sensitive to the line-of-sight magnetic field in conjunction with the electron density. This contribution highlights diagnostic possibilities of inferring the magnetic field (or absence thereof) in and around wind-blown bubbles from the Faraday effect. Three cases are described as illustrations: a stellar toroidal magnetic field, a shocked interstellar magnetic field, and an interstellar magnetic field within an ionized bubble.

Continuum Polarization In Circumstellar Media, Richard Ignace

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See http://www.asu.cas.cz/~wg2prague/

Convection, Granulation, And Period Jitter In Classical Cepheids., Hilding Neilson, Richard Ignace

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Analyses of recent observations of the sole classical Cepheid in the Kepler field, V1154 Cygni, found random changes of about 30 min in the pulsation period. These period changes challenge standard theories of pulsation and evolution because the period change is non-secular, and explaining this period jitter is necessary for understanding stellar evolution and the role of Cepheids as precise standard candles. We suggest that convection and convective hot spots can explain the observed period jitter. Convective hot spots alter the timing of flux maximum and minimum in the Cepheid light curve, hence change the measured pulsation period. We present …