scholarly journals DIAGNOSTIC LINE EMISSION FROM EXTREME ULTRAVIOLET AND X-RAY-ILLUMINATED DISKS AND SHOCKS AROUND LOW-MASS STARS

2009 ◽  
Vol 703 (2) ◽  
pp. 1203-1223 ◽  
Author(s):  
David Hollenbach ◽  
U. Gorti
Keyword(s):  
Extreme Ultraviolet ◽  
Line Emission ◽  
Low Mass Stars ◽  
X Ray ◽  
Low Mass

Implications of stellar activity for exoplanetary atmospheres

2010 ◽  
Vol 9 (4) ◽  
pp. 239-243 ◽  
Author(s):  
P. Odert ◽  
M. Leitzinger ◽  
A. Hanslmeier ◽  
H. Lammer ◽  
M.L. Khodachenko ◽  
...  
Keyword(s):  
Extreme Ultraviolet ◽  
Planetary Atmospheres ◽  
Young Star ◽  
Young Stars ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
X Ray ◽  
History Of ◽  
Low Mass ◽  
Exoplanetary Atmospheres

AbstractStellar X-ray and extreme ultraviolet (XUV) radiation is an important driver of the escape of planetary atmospheres. Young stars emit high XUV fluxes that decrease as they age. Since the XUV emission of a young star can be orders of magnitude higher compared to an older one, this evolution has to be taken into account when studying the mass-loss history of a planet. The temporal decrease of activity is closely related to the operating magnetic dynamo, which depends on rotation and convection in Sun-like stars. Using a sample of nearby M dwarfs, we study the relations between age, rotation and activity and discuss the influence on planets orbiting these low-mass stars.

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> 10 keV is likely due to fluorescence outside the He II ionization front.

scholarly journals X-Ray Detection of Brown Dwarfs with Chandra

2003 ◽  
Vol 211 ◽  
pp. 447-450 ◽  
Author(s):  
Scott J. Wolk
Keyword(s):  
Brown Dwarfs ◽  
Stellar Clusters ◽  
Brown Dwarf ◽  
Low Mass Stars ◽  
X Ray ◽  
Low Mass ◽  
Vast Range

I review recent observations of brown dwarfs by the Chandra X-ray Observatory. These observations fall in 2 categories, young stellar clusters which contain brown dwarfs and brown dwarf candidates and directed pointings at brown dwarfs and very low mass stars. Surprisingly, there are already over 60 published detections of brown dwarfs by Chandra. A review of the X–ray characteristics shows these objects are subject to flaring and their temperatures and luminosities have a vast range which is related to age.

scholarly journals INVESTIGATION OF DENSE GAS TOWARDS RELATIVISTIC OUTFLOW SOURCES

2014 ◽  
Vol 28 ◽  
pp. 1460198
Author(s):  
J. HAWKES ◽  
G. ROWELL ◽  
B. DAWSON ◽  
F. AHARONIAN ◽  
M. BURTON ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Line Emission ◽  
High Energy ◽  
Dense Gas ◽  
Relativistic Jets ◽  
Hii Region ◽  
X Ray ◽  
Stellar Cluster ◽  
Radio Recombination Line ◽  
Low Mass

We probe the interstellar medium towards the objects Circinus X-1, a low-mass X-ray binary with relativistic jets; and the highly energetic Westerlund 2 stellar cluster, which is located towards TeV gamma-ray emission and interesting arc- and jet-like features seen in Nanten 12CO data. We have mapped both regions with the Mopra radio telescope, in 7 mm and 12 mm wavebands, looking for evidence of disrupted/dense gas caused by the interaction between high energy outflows and the ISM. Towards Westerlund 2, peaks in CS(J=1-0) emission indicate high density gas towards the middle of the arc and the endpoint of the jet; and radio recombination line emission is seen overlapping the coincident HII region RCW49. Towards Circinus X-1, 12CO(J = 1-0) Nanten data reveals three molecular clouds that lie in the region of Cir X-1. Gas parameters for each cloud are presented here.

The X-Ray View of the Low-Mass Stars in the Solar Neighborhood

1995 ◽  
Vol 450 ◽  
pp. 392 ◽  
Author(s):  
Juergen H. M. M. Schmitt ◽  
Thomas A. Fleming ◽  
Mark S. Giampapa
Keyword(s):  
Solar Neighborhood ◽  
Low Mass Stars ◽  
X Ray ◽  
Low Mass

scholarly journals News on the X-ray emission from hot subdwarf stars

2017 ◽  
Vol 26 (1) ◽  
Author(s):  
Nicola La Palombara ◽  
Sandro Mereghetti
Keyword(s):  
Neutron Star ◽  
Binary Systems ◽  
High Sensitivity ◽  
Research Area ◽  
X Rays ◽  
Low Mass Stars ◽  
X Ray ◽  
Low Mass ◽  
Hot Subdwarfs ◽  
Weak Winds

AbstractIn latest years, the high sensitivity of the instruments on-board the XMM-Newton and Chandra satellites allowed us to explore the properties of the X-ray emission from hot subdwarf stars. The small but growing sample of X-ray detected hot subdwarfs includes binary systems, in which the X-ray emission is due to wind accretion onto a compact companion (white dwarf or neutron star), as well as isolated sdO stars, in which X-rays are probably due to shock instabilities in the wind. X-ray observations of these low-mass stars provide information which can be useful for our understanding of the weak winds of this type of stars and can lead to the discovery of particularly interesting binary systems. Here we report the most recent results we have recently obtained in this research area.

scholarly journals The high-energy radiation environment of the habitable-zone super-Earth LHS 1140b

2019 ◽  
Vol 627 ◽  
pp. A144 ◽  
Author(s):  
R. Spinelli ◽  
F. Borsa ◽  
G. Ghirlanda ◽  
G. Ghisellini ◽  
S. Campana ◽  
...  
Keyword(s):  
Spectral Energy Distribution ◽  
High Energy ◽  
Radiation Environment ◽  
Habitable Zone ◽  
Low Mass Stars ◽  
High Energy Radiation ◽  
Energy Radiation ◽  
X Ray ◽  
Near Ultraviolet ◽  
Low Mass

Context. In the last few years many exoplanets in the habitable zone (HZ) of M-dwarfs have been discovered, but the X-ray/UV activity of cool stars is very different from that of our Sun. The high-energy radiation environment influences the habitability, plays a crucial role for abiogenesis, and impacts the chemistry and evolution of planetary atmospheres. LHS 1140b is one of the most interesting exoplanets discovered. It is a super-Earth-size planet orbiting in the HZ of LHS 1140, an M4.5 dwarf at ~15 parsecs. Aims. In this work, we present the results of the analysis of a Swift X-ray/UV observing campaign. We characterize for the first time the X-ray/UV radiation environment of LHS 1140b. Methods. We measure the variability of the near ultraviolet (NUV) flux and estimate the far ultraviolet (FUV) flux with a correlation between FUV1344−1786Å and NUV1771−2831Å flux obtained using the sample of low-mass stars in the GALEX archive. We highlight the presence of a dominating X-ray source close to the J2000 coordinates of LHS 1140, characterize its spectrum, and derive an X-ray flux upper limit for LHS 1140. We find that this contaminant source could have influenced the previously estimated spectral energy distribution. Results. No significant variation of the NUV1771−2831Å flux of LHS 1140 is found over 3 months, and we do not observe any flare during the 38 ks on the target. LHS 1140 is in the 25th percentile of least variable M4-M5 dwarfs of the GALEX sample. Analyzing the UV flux experienced by the HZ planet LHS 1140b, we find that outside the atmosphere it receives a NUV1771−2831Å flux <2% with respect to that of the present-day Earth, while the FUV1344−1786Å/NUV1771−2831Å ratio is ~100–200 times higher. This represents a lower limit to the true FUV/NUV ratio since the FUV1344−1786Å band does not include Lyman-alpha, which dominates the FUV output of low-mass stars. This is a warning for future searches for biomarkers, which must take into account this high ratio. Conclusions. The relatively low level and stability of UV flux experienced by LHS 1140b should be favorable for its present-day habitability.

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