scholarly journals Magnetic activity, high-energy radiation and variability: from young solar analogs to low-mass objects

2009 ◽  
Vol 5 (S264) ◽  
pp. 375-384
Author(s):  
Manuel Güdel
Keyword(s):  
Extreme Ultraviolet ◽  
High Energy ◽  
Magnetic Activity ◽  
Energy Output ◽  
Stellar Winds ◽  
High Energy Radiation ◽  
X Ray ◽  
Cool Stars ◽  
Low Mass ◽  
Solar Analogs

AbstractMagnetic activity on cool stars expresses itself in a bewildering variety of radiative and particle output originating from magnetic regions between the photosphere and the corona. Given its origin in evolving magnetic fields, most of this output is variable in time. Radiation in the ultraviolet, the extreme ultraviolet, and the X-ray ranges are important for heating and ionizing upper planetary atmospheres and thus driving atmospheric evaporation. Additionally, stellar winds interact with the upper atmospheres and may lead to further erosion. The stellar high-energy output is therefore a prime factor in determining habitability of planets. We summarize our knowledge of magnetic activity in young solar analogs and lower-mass stars and show how the stellar output changes on evolutionary timescales.

scholarly journals Non thermal emission from T Tauri stars

2010 ◽  
Vol 6 (S275) ◽  
pp. 404-405
Author(s):  
María V. del Valle ◽  
Gustavo E. Romero
Keyword(s):  
Main Sequence ◽  
Thermal Emission ◽  
High Energy ◽  
Magnetic Activity ◽  
T Tauri Stars ◽  
Main Sequence Stars ◽  
High Energy Radiation ◽  
X Ray ◽  
T Tauri ◽  
Low Mass

AbstractT Tauri stars are low mass, pre-main sequence stars. These objects are surrounded by an accretion disk and present strong magnetic activity. T Tauri stars are copious emitters of X-ray emission which belong to powerful magnetic reconnection events. Strong magnetospheric shocks are likely outcome of massive reconnection. Such shocks can accelerate particles up to relativistic energies through Fermi mechanism. We present a model for the high-energy radiation produced in the environment of T Tauri stars. We aim at determining whether this emission is detectable. If so, the T Tauri stars should be very nearby.

scholarly journals Constraining X-ray-Induced Photoevaporation of Protoplanetary Disks Orbiting Low-Mass Stars

2015 ◽  
Vol 10 (S314) ◽  
pp. 203-204
Author(s):  
Kristina M. Punzi ◽  
Joel H. Kastner ◽  
David Rodriguez ◽  
David A. Principe ◽  
Laura Vican
Keyword(s):  
Protoplanetary Disks ◽  
High Energy ◽  
Magnetic Activity ◽  
Young Star ◽  
Low Mass Stars ◽  
High Energy Radiation ◽  
X Ray ◽  
Radiation Fields ◽  
Low Mass ◽  
M Stars

AbstractLow-mass, pre-main sequence stars possess intense high-energy radiation fields as a result of their strong stellar magnetic activity. This stellar UV and X-ray radiation may have a profound impact on the lifetimes of protoplanetary disks. We aim to constrain the X-ray-induced photoevaporation rates of protoplanetary disks orbiting low-mass stars by analyzing serendipitous XMM-Newton and Chandra X-ray observations of candidate nearby (D < 100 pc), young (age < 100 Myr) M stars identified in the GALEX Nearby Young-Star Survey (GALNYSS).

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.

scholarly journals The Sun in time: age, rotation, and magnetic activity of the Sun and solar-type stars and effects on hosted planets

2008 ◽  
Vol 4 (S258) ◽  
pp. 395-408 ◽  
Author(s):  
Edward F. Guinan ◽  
Scott G. Engle
Keyword(s):  
Main Sequence ◽  
High Energy ◽  
Magnetic Activity ◽  
The Sun ◽  
X Ray ◽  
Multi Wavelength ◽  
Solar Type ◽  
Rotation Age ◽  
Energy Emissions ◽  
Solar Analogs

AbstractMulti-wavelength studies of solar analogs (G0–5 V stars) with ages from ~50 Myr to 9 Gyr have been carried out as part of the “Sun in Time” program for nearly 20 yrs. From these studies it is inferred that the young (ZAMS) Sun was rotating more than 10× faster than today. As a consequence, young solar-type stars and the early Sun have vigorous magnetohydrodynamic (MHD) dynamos and correspondingly strong coronal X-ray and transition region/chromospheric FUV–UV emissions (up to several hundred times stronger than the present Sun). Also, rotational modulated, low amplitude light variations of young solar analogs indicate the presence of large starspot regions covering ~5–30% of their surfaces. To ensure continuity and homogeneity for this program, we use a restricted sample of G0–5 V stars with masses, radii, Teff, and internal structure (i.e. outer convective zones) closely matching those of the Sun. From these analogs we have determined reliable rotation-age-activity relations and X-ray–UV (XUV) spectral irradiances for the Sun (or any solar-type star) over time. These XUV irradiance measures serve as input data for investigating the photo-ionization and photo-chemical effects of the young, active Sun on the paleo-planetary atmospheres and environments of solar system planets. These measures are also important to study the effects of these high energy emissions on the numerous exoplanets hosted by solar-type stars of different ages. Recently we have extended the study to include lower mass, main-sequence (dwarf) dK and dM stars to determine relationships among their rotation spin-down rates and coronal and chromospheric emissions as a function of mass and age. From rotation-age-activity relations we can determine reliable ages for main-sequence G, K, M field stars and, subsequently, their hosted planets. Also inferred are the present and the past XUV irradiance and plasma flux exposures that these planets have endured and the suitability of the hosted planets to develop and sustain life.

scholarly journals Proxima Centauri – the nearest planet host observed simultaneously with AstroSat, Chandra, and HST

2020 ◽  
Vol 498 (3) ◽  
pp. 3658-3663
Author(s):  
S Lalitha ◽  
J H M M Schmitt ◽  
K P Singh ◽  
P C Schneider ◽  
R O Parke Loyd ◽  
...  
Keyword(s):  
Spectral Type ◽  
High Energy ◽  
Mass Star ◽  
Habitable Zone ◽  
High Energy Radiation ◽  
Energy Radiation ◽  
X Ray ◽  
Coronal Activity ◽  
Low Mass

ABSTRACT Our nearest stellar neighbour, Proxima Centauri, is a low-mass star with spectral type dM5.5 and hosting an Earth-like planet orbiting within its habitable zone. However, the habitability of the planet depends on the high-energy radiation of the chromospheric and coronal activity of the host star. We report the AstroSat, Chandra, and HST observation of Proxima Centauri carried out as part of the multiwavelength simultaneous observational campaign. Using the soft X-ray data, we probe the different activity states of the star. We investigate the coronal temperatures, emission measures and abundance. Finally, we compare our results with earlier observations of Proxima Centauri.

scholarly journals High Energy Radiation from Spider Pulsars

Galaxies ◽  
2019 ◽  
Vol 7 (4) ◽  
pp. 93 ◽  
Author(s):  
Chung Yue Hui ◽  
Kwan Lok Li
Keyword(s):  
High Energy ◽  
X Rays ◽  
The Novel ◽  
Large Area ◽  
High Energy Radiation ◽  
X Ray ◽  
Compact Binaries ◽  
Low Mass ◽  
Γ Rays ◽  
Γ Ray

The population of millisecond pulsars (MSPs) has been expanded considerably in the last decade. Not only is their number increasing, but also various classes of them have been revealed. Among different classes of MSPs, the behaviours of black widows and redbacks are particularly interesting. These systems consist of an MSP and a low-mass companion star in compact binaries with an orbital period of less than a day. In this article, we give an overview of the high energy nature of these two classes of MSPs. Updated catalogues of black widows and redbacks are presented and their X-ray/ γ -ray properties are reviewed. Besides the overview, using the most updated eight-year Fermi Large Area Telescope point source catalog, we have compared the γ -ray properties of these two MSP classes. The results suggest that the X-rays and γ -rays observed from these MSPs originate from different mechanisms. Lastly, we will also mention the future prospects of studying these spider pulsars with the novel methodologies as well as upcoming observing facilities.

scholarly journals X-exoplanets: an X-ray and EUV database for exoplanets

2009 ◽  
Vol 5 (S264) ◽  
pp. 478-483 ◽  
Author(s):  
J. Sanz-Forcada ◽  
D. García-Álvarez ◽  
A. Velasco ◽  
E. Solano ◽  
I. Ribas ◽  
...  
Keyword(s):  
Main Sequence ◽  
Extreme Ultraviolet ◽  
High Energy ◽  
Atmospheric Composition ◽  
X Rays ◽  
High Energy Radiation ◽  
X Ray ◽  
Euv Emission ◽  
Synthetic Spectra ◽  
Parent Star

AbstractExtreme Ultraviolet (EUV) and X-ray emission is of great importance in several phenomena related to the formation of planetary systems and the atmospheres of planets. The atmospheric composition, and the mass of an exoplanet, are partly dependent on the X-ray and EUV radiation received during the first stages of formation and even during main sequence of the star. Biological life developing on exoplanets would depend severely on the high energy radiation arriving from its parent star.Here we present a database of the X-ray and EUV emission of all the stars currently known to host exoplanets. The archive is public and accessible through the Spanish Virtual Observatory (SVO). The database gives the user the option to download observed X-rays and EUV spectra. Synthetic spectra covering the spectral range 1–912 Å are also available (present day telescopes do not give access to the EUV range at λ > 180 Å). These spectra are created using coronal models after fitting observed spectra.

scholarly journals V479 And: CV, LMXB, or Symbiotic?

2011 ◽  
Vol 7 (S281) ◽  
pp. 113-116
Author(s):  
Diego González Buitrago ◽  
Gagik Tovmassian ◽  
Juan Echevarría ◽  
Sergey Zharikov ◽  
Takamitsu Miyaji ◽  
...  
Keyword(s):  
Orbital Period ◽  
Main Sequence ◽  
Compact Object ◽  
Close Binary System ◽  
Close Binary ◽  
Stellar Winds ◽  
Primary Star ◽  
Giant Star ◽  
X Ray ◽  
Low Mass

AbstractV479 And is a 14.26 hour, close binary system, comprised of a G8-K0 star departing from the main sequence and a compact primary star accreting matter from the donor. The object is an X-ray source, modulated with the orbital period. This, and the presence of an intense He II line, leads us to speculate that the compact object is a magnetic white dwarf. However, we do not find strong constraints on the upper mass limit of the compact object, and we may have a neutron star in a low mass X-ray binary instead of a cataclysmic variable. The orbital period is certainly too short for the donor star to be an evolved giant star, so classifying this object as a symbiotic binary may be a big stretch; however there is an evidence that the mass transfer occurs via stellar winds, rather than through the L1 point of Roche filling secondary, a phenomenon more common for symbiotic stars.

scholarly journals The extreme ultraviolet and X-ray Sun in Time: High-energy evolutionary tracks of a solar-like star

2015 ◽  
Vol 577 ◽  
pp. L3 ◽  
Author(s):  
Lin Tu ◽  
Colin P. Johnstone ◽  
Manuel Güdel ◽  
Helmut Lammer
Keyword(s):  
Extreme Ultraviolet ◽  
High Energy ◽  
X Ray

scholarly journals Photo-evaporation of close-in gas giants orbiting around G and M stars

2019 ◽  
Vol 624 ◽  
pp. A101 ◽  
Author(s):  
Daniele Locci ◽  
Cesare Cecchi-Pestellini ◽  
Giuseppina Micela
Keyword(s):  
Extreme Ultraviolet ◽  
Dynamical Evolution ◽  
High Energy ◽  
Electron Content ◽  
Mass Star ◽  
X Rays ◽  
Atmospheric Escape ◽  
Low Mass ◽  
M Stars ◽  
The Stability

Context. X-rays and extreme ultraviolet radiation impacting a gas produce a variety of effects that, depending on the electron content, may provide significant heating of the illuminated region. In a planetary atmosphere of solar composition, stellar high energy radiation can heat the gas to very high temperatures and this could affect the stability of planetary atmospheres, in particular for close-in planets. Aims. We investigate the variations with stellar age in the occurring frequency of gas giant planets orbiting G and M stars, taking into account that the high energy luminosity of a low mass star evolves in time, both in intensity and hardness. Methods. Using the energy-limited escape approach we investigated the effects induced by the atmospheric mass loss on giant exoplanet distribution that is initially flat, at several distances from the parent star. We followed the dynamical evolution of the planet atmosphere, tracking the departures from the initial profile due to the atmospheric escape, until it reaches the final mass-radius configuration. Results. We find that a significant fraction of low mass Jupiter-like planets orbiting with periods lower than ~3.5 days either vaporize during the first billion years or lose a relevant part of their atmospheres. The planetary initial mass profile is significantly distorted; in particular, the frequency of occurrence of gas giants, less massive than 2 MJ, around young stars can be considerably greater than their occurrence around older stellar counterparts.

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