scholarly journals Short-term variability and mass loss in Be stars

2020 ◽  
Vol 635 ◽  
pp. A140 ◽  
Author(s):  
C. C. Borre ◽  
D. Baade ◽  
A. Pigulski ◽  
D. Panoglou ◽  
A. Weiss ◽  
...  
Keyword(s):  
Spiral Structure ◽  
Line Emission ◽  
Amplitude Distribution ◽  
Optical Variability ◽  
Radial Pulsation ◽  
Be Stars ◽  
Short Term ◽  
Period Range ◽  
Rapid Rotation ◽  
X Ray

Context. Be stars are physically complex systems that continue to challenge theory to understand their rapid rotation, complex variability, and decretion disks. γ Cassiopeiae (γ Cas) is one such star but is even more curious because of its unexplained hard thermal X-ray emission. Aims. We aim to examine the optical variability of γ Cas and thereby to shed more light on its puzzling behaviour. Methods. We analysed 321 archival Hα spectra from 2006 to 2017 to search for frequencies corresponding to the 203.5 day orbit of the companion. Space photometry from the SMEI satellite from 2003 to 2011 and the BRITE-Constellation of nano-satellites from 2015 to 2019 were investigated in the period range from a couple of hours to a few days. Results. The orbital period of the companion of 203.5 days is confirmed with independent measurements from the structure of the Hα line emission. A strong blue versus red asymmetry in the amplitude distribution across the Hα emission line could hint at a spiral structure in the decretion disk. With the space photometry, the known frequency of 0.82 d−1 is confirmed in data from the early 2000s. A higher frequency of 2.48 d−1 is present in the data from 2015 to 2019 and possibly in the early 2000s as well. A third frequency at 1.25 d−1 is proposed to exist in both SMEI and BRITE data. Seemingly, only a non-radial pulsation interpretation can explain all three variations. The two higher frequencies are incompatible with rotation.

scholarly journals Photometric studies of Be star variability

1994 ◽  
Vol 162 ◽  
pp. 299-300
Author(s):  
John R. Percy
Keyword(s):  
Time Scales ◽  
Balmer Line ◽  
Radial Pulsation ◽  
Be Stars ◽  
Photometric Study ◽  
Short Term ◽  
Hot Stars ◽  
Be Star ◽  
Short Term Variability

Be stars are hot stars which have shown emission in at least one Balmer line on at least one occasion. As the definition implies, the Be phenomenon can be variable with time: on time scales of days to decades as the circumstellar disc develops and disperses; on time scales of days to months in a few Be stars which are interacting binaries; on time scales of 0.2 to 2 days due to non-radial pulsation or possibly rotation. The Be stars are worthy of photometric study because they are bright and numerous; the nature of the short-term variability is not yet agreed upon; the cause of the development of the disc - and its relationship to the short-term variability - is also not yet known.

scholarly journals Photometric and H-Alpha Variability in Some Be Stars

1987 ◽  
Vol 92 ◽  
pp. 101-103
Author(s):  
S. Catalano ◽  
G. Umana
Keyword(s):  
Magnetic Fields ◽  
Time Scales ◽  
Time Scale ◽  
Small Amplitude ◽  
Rotation Period ◽  
Light Curves ◽  
Radial Pulsation ◽  
Be Stars ◽  
Relative Movement ◽  
Short Term

Short-term variations, typically with small amplitude (Δm < 0.1 mag.), time-scales of hours or near one day and in many cases correlated with the rotation period have been found to be commonplace among Be stars (see Harmanec and Pavlovski 1983 for review and papers). Radial and non-radial pulsation modes have been proposed to explain this variability. However, the light curves are often double-peaked, at first suggesting the stars may have large organized dipole magnetic fields and spots not unlike those in the Ap or Bp stars (Harmanec 1983). These rotationally modulated variations are not stable, and seem to vary in both amplitude and period in the sense that intervals with well defined light curves alternate with intervals when variations are absent. This phenomenon is very reminiscent of formation and apparent relative movement in longitude of spots (groups) in some RS CVn binaries (Catalano 1983, Rodono 1986), but on a much more rapid time scale.

scholarly journals Non-Radial Pulsation In Be Stars

1986 ◽  
Vol 7 ◽  
pp. 265-272
Author(s):  
John R. Percy
Keyword(s):  
Mass Transfer ◽  
Critical Velocity ◽  
Main Sequence ◽  
Radial Pulsation ◽  
Be Stars ◽  
Hydrogen Line ◽  
Main Sequence Stars ◽  
Rapid Rotation ◽  
B Stars ◽  
Effective Gravity

Be stars are B stars in which emission has been observed in at least one hydrogen line on at least one occasion. Some Be stars are pre-main-sequence stars, mass-transfer binaries, or supergiant stars with extended atmospheres. The majority, however, are classical Be stars: single stars on or near the main sequence. An important characteristic of these stars seems to be their rapid rotation – close to but not at the “critical” velocity at which the effective gravity vanishes at the equator.

Long-term optical variability of Her X-1

2018 ◽  
Vol 14 (S346) ◽  
pp. 239-241
Author(s):  
T. İçli ◽  
D. Koçak ◽  
K. Yakut
Keyword(s):  
Neutron Star ◽  
Binary System ◽  
Orbital Period ◽  
Optical Variability ◽  
National Observatory ◽  
Short Term ◽  
X Ray ◽  
Robotic Telescope

AbstractLong-term and short-term multicolor photometric variations of the X-ray binary system Her X-1 (HZ Her) has been studied. We obtained new VRI observations of the system by using the 60cm Robotic telescope at the TÜBİTAK National Observatory (TUG) in 2018. Using newly obtained data, we modified the orbital period of the binary system with a neutron star component.

scholarly journals Short-term variability and mass loss in Be stars VI. Frequency groups in γ Cas detected by TESS

2020 ◽  
Author(s):  
Jonathan Labadie-Bartz ◽  
Dietrich Baade ◽  
Alex C Carciofi ◽  
Amanda Rubio ◽  
Thomas Rivinius ◽  
...  
Keyword(s):  
Low Frequency ◽  
Internal Gravity Waves ◽  
Total Power ◽  
Radial Pulsation ◽  
Be Stars ◽  
Short Term ◽  
Dominant Feature ◽  
Major Property ◽  
Combination Frequencies

Abstract In photometry of γ Cas (B0.5 IVe) from the SMEI and BRITE-Constellation satellites, indications of low-order non-radial pulsation have recently been found, which would establish an important commonality with the class of classical Be stars at large. New photometry with the TESS satellite has detected three frequency groups near 1.0 (g1), 2.4 (g2), and 5.1 (g3) d−1, respectively. Some individual frequencies are nearly harmonics or combination frequencies but not exactly so. Frequency groups are known from roughly three quarters of all classical Be stars and also from pulsations of β Cep, SPB, and γ Dor stars and, therefore, firmly establish γ Cas as a non-radial pulsator. The total power in each frequency group is variable. An isolated feature exists at 7.57 d−1 and, together with the strongest peaks in the second and third groups ordered by increasing frequency (g2 and g3), is the only one detected in all three TESS sectors. The former long-term 0.82 d−1 variability would fall into g1 and has not returned at a significant level, questioning its attribution to rotational modulation. Low-frequency stochastic variability is a dominant feature of the TESS light curve, possibly caused by internal gravity waves excited at the core-envelope interface. These are known to be efficient at transporting angular momentum outward, and may also drive the oscillations that constitute g1 and g2. The hard X-ray flux of γ Cas is the only remaining major property that distinguishes this star from the class of classical Be stars.

scholarly journals Three discoveries of γ Cas analogues from dedicated XMM–Newton observations of Be stars

2020 ◽  
Vol 493 (2) ◽  
pp. 2511-2517 ◽  
Author(s):  
Yaël Nazé ◽  
Christian Motch ◽  
Gregor Rauw ◽  
Shami Kumar ◽  
Jan Robrade ◽  
...  
Keyword(s):  
Spectral Characterization ◽  
Spectral Information ◽  
X Rays ◽  
Be Stars ◽  
Spectral Variability ◽  
Short Term ◽  
X Ray ◽  
Long Term Variations

ABSTRACT In the last years, a peculiarity of some Be stars – their association with unusually hard and intense X-ray emission – was shown to extend beyond a mere few cases. In this paper, we continue our search for new cases by performing a limited survey of 18 Be stars using XMM–Newton. The targets were selected either on the basis of a previous X-ray detection (exosat,rosat, XMM-slew survey) without spectral information available or because of the presence of a peculiar spectral variability. Only two targets remain undetected in the new observations and three other stars display only faint and soft X-rays. Short-term and/or long-term variations were found in one third of the sample. The spectral characterization of the X-ray brightest 13 stars of the sample led to the discovery of three new γ Cas (HD 44458, HD 45995, and V558 Lyr), bringing the total to 25 known cases, and another γ Cas candidate (HD 120678), bringing the total to two.

scholarly journals Swift monitoring of NGC 5548: X-ray reprocessing and short-term UV/optical variability

2014 ◽  
Vol 444 (2) ◽  
pp. 1469-1474 ◽  
Author(s):  
I. M. McHardy ◽  
D. T. Cameron ◽  
T. Dwelly ◽  
S. Connolly ◽  
P. Lira ◽  
...  
Keyword(s):  
Optical Variability ◽  
Short Term ◽  
X Ray ◽  
Ngc 5548

Iron K-Line Emission from X-Ray Binaries

1988 ◽  
Vol 102 ◽  
pp. 47-50
Author(s):  
K. Masai ◽  
S. Hayakawa ◽  
F. Nagase
Keyword(s):  
Accretion Disk ◽  
Radiative Recombination ◽  
Characteristic Temperature ◽  
Line Emission ◽  
Ionization Front ◽  
Continuum Radiation ◽  
X Ray ◽  
Low Mass ◽  
X Ray Binaries

AbstractEmission mechanisms of the iron Kα-lines in X-ray binaries are discussed in relation with the characteristic temperature Txof continuum radiation thereof. The 6.7 keV line is ascribed to radiative recombination followed by cascades in a corona of ∼ 100 eV formed above the accretion disk. This mechanism is attained for Tx≲ 10 keV as observed for low mass X-ray binaries. The 6.4 keV line observed for binary X-ray pulsars with Tx&gt; 10 keV is likely due to fluorescence outside the He II ionization front.

scholarly journals GCT-08. PROTON BEAM RADIOTHERAPY FOR PEDIATRIC AND YOUNG-ADULT PATIENTS WITH INTRACRANIAL GERM CELL TUMOR

2020 ◽  
Vol 22 (Supplement_3) ◽  
pp. iii329-iii329
Author(s):  
Minako Sugiyama ◽  
Takayuki Hashimoto ◽  
Takashi Mori ◽  
Kazuya Hara ◽  
Yukayo Terashita ◽  
...  
Keyword(s):  
Young Adult ◽  
Adverse Events ◽  
Germ Cell ◽  
Cell Count ◽  
Proton Beam ◽  
Adult Patients ◽  
Short Term ◽  
Intracranial Germ Cell Tumor ◽  
X Ray ◽  
Proton Beam Radiotherapy

Abstract BACKGROUND To reduce treatment-related adverse events in pediatric and young-adult patients with brain tumors, proton beam radiotherapy (PBT) has recently been performed instead of conventional X-ray radiotherapy. However, whether PBT is as effective as X-ray radiotherapy has not been sufficiently investigated, especially in patients receiving whole-ventricular irradiation. METHODS We report a retrospective observation of 15 patients with intracranial germ cell tumors (GCT), who received PBT at our institution from April 2014 to September 2019. We evaluated their clinical course, short-term adverse events, and prognosis. RESULTS/ CONCLUSION Fifteen patients (9 males and 6 females; median age 13 years) who received PBT following induction chemotherapy were analyzed. Nine patients received 23.4–27.0 GyE of whole-ventricular irradiation due to GCT in the pituitary gland, pineal body, or hypothalamic area. Three patients received 23.4 GyE of whole-brain irradiation: one of them had boost irradiation for basal ganglia. Three patients received 30.6 GyE of craniospinal irradiation (CSI). Six of the 15 patients experienced nausea (grade 2, according to the CTCAE version 4.0). Four patients, including two who received CSI, showed myelosuppression: decrease in white blood cell count, lymphocyte cell count, and neutrophil count (grade 3). No other severe short-term adverse events of &gt;grade 2 was observed in any of the patients. At a median follow-up of 21 months (2-62 months) after irradiation. all patients are alive without recurrence. Our results may be encouraging and further investigations with a larger scale is warranted.

scholarly journals Silicon in the solar corona

1965 ◽  
Vol 23 ◽  
pp. 115-123
Author(s):  
K. G. Widing ◽  
J. R. Porter
Keyword(s):  
Solar Corona ◽  
Relative Intensity ◽  
Line Emission ◽  
X Ray ◽  
Resonance Transitions ◽  
Spectral Ranges

Resonance lines of coronal ions of silicon are prominent in the spectral ranges 40–62 Å and 254–356 Å.An unexpected feature of the soft X-ray spectrum is the weakness or absence of the resonance lines of iron in ionization stages XI through XV.A second feature is the prominence of lines of the type (3d → 2p) relative to the resonance transitions (3p → 2s) in Li-like and Beryllium-like spectra. It is suggested that the upper levels (3d) are excited by quadrupole collisions from the ground 2s or 2s2levels.The intensity of the soft X-ray lines relative to the resonance lines in the 300 Å region seems to be more consistent with temperatures well above one million degrees than with temperatures as low as 700000°K, but the data are not adequate for a precise comparison. The relative intensity of the line emission from the various stages of silicon ionization may be interpreted as indicating that the ionization of silicon peaks in stages IX and X.The abundances of C, Mg, S, and Al relative to silicon do not seem to be greatly different from the chromospheric abundances reported by Pottasch or with the photospheric abundances.

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