scholarly journals Evolution of Stellar Activity in Early Post-Main-Sequence Phases

1993 ◽  
Vol 137 ◽  
pp. 648-650
Author(s):  
A. Maggio ◽  
S. Sciortino ◽  
L. Bianchi ◽  
F.R. Harnden ◽  
R. Rosner
Keyword(s):  
Spectral Type ◽  
Main Sequence ◽  
Activity Level ◽  
Sensitivity Threshold ◽  
Moderate Increase ◽  
X Rays ◽  
Late Type ◽  
Lower Mass ◽  
X Ray ◽  
Radiative Emission

We present preliminary observational evidences on the variation of the activity level in late type stars, during the evolutionary phases on the main sequence and beyond. We have selected a sample of 51 stars (Fig. 1), lying mostly along evolutionary tracks between 1.3 and 1.7 solar masses, which have been observed in soft X-rays with the Einstein Observatory, and in UV with IUE (Maggio et al. 1990; Haisch et al.1990). Two ROSAT targets, and four new IUE observations are also included.We find that the radiative emission from the outer atmospheres of stars with M > 1.6M⊙ seems to behave differently than for stars with lower mass.On the main sequence, the X-ray luminosity of most stars with B-V < 0.42 (spectral type F3) is relatively low, at Lx ~ 3 × 1028erg s-1 (Fig. 2). In the early evolutionary phases beyond the main sequence, the X-ray luminosity of the higher mass stars tend to increase sistematically up to ~ 1030erg s-1, while the lower mass stars show an initial moderate increase followed by a drop, at B-V ~ 0.6, below our sensitivity threshold.

scholarly journals Observations of Magnetic Fields on Late-Type Stars

1983 ◽  
Vol 102 ◽  
pp. 1-22
Author(s):  
Geoffrey W. Marcy
Keyword(s):  
Magnetic Fields ◽  
Flux Tube ◽  
Spectral Type ◽  
Transport Mechanism ◽  
Main Sequence ◽  
Energy Transport ◽  
Slow Mode ◽  
Late Type ◽  
Main Sequence Stars ◽  
X Ray

The “Robinson” method for measuring magnetic fields on solar- and late-type stars is reviewed. The results of such measurements for a sample of 29 G and K main-sequence stars are presented. The area covering-factors of magnetic regions are greater in the K dwarfs than in the G dwarfs, but no spectral-type dependence is found for the field strengths, contrary to expectations of some flux-tube models. The dependence of Ca II H and K emission on magnetic fields and Teff is consistent with theoretical expectations for “slow-mode” mhd wave-generation rates, but inconsistent with those of other mhd modes. Coronal soft X-ray fluxes correlate well with the magnetic fields, and it is argued that Alfvén waves are the likely energy-transport mechanism. Surface magnetic fluxes vary with rotation as , depending on spectral type.

scholarly journals Updated X-ray view of the Hyades cluster

2020 ◽  
Vol 640 ◽  
pp. A66 ◽  
Author(s):  
S. Freund ◽  
J. Robrade ◽  
P. C. Schneider ◽  
J. H. M. M. Schmitt
Keyword(s):  
Main Sequence ◽  
Distribution Functions ◽  
X Rays ◽  
Stellar Rotation ◽  
Detection Rates ◽  
X Ray ◽  
Rotation Periods ◽  
Hyades Cluster ◽  
Bona Fide ◽  
Tidal Tails

Aims. We revisit the X-ray properties of the main sequence Hyades members and the relation between X-ray emission and stellar rotation. Methods. As an input catalog for Hyades members, we combined three recent Hyades membership lists derived from Gaia DR2 data that include the Hyades core and its tidal tails. We searched for X-ray detections of the main sequence Hyades members in the ROSAT all-sky survey, and pointings from ROSAT, the Chandra X-Ray Observatory, and XMM-Newton. Furthermore, we adopted rotation periods derived from Kepler’s K2 mission and other resources. Results. We find an X-ray detection for 281 of 1066 bona fide main sequence Hyades members and provide statistical upper limits for the undetected sources. The majority of the X-ray detected stars are located in the Hyades core because of its generally smaller distance to the Sun. F- and G-type stars have the highest detection fraction (72%), while K- and M-type dwarfs have lower detection rates (22%). The X-ray luminosities of the detected members range from ∼2 × 1027 erg s−1 for late M-type dwarfs to ∼2 × 1030 erg s−1 for active binaries. The X-ray luminosity distribution functions formally differ for the members in the core and tidal tails, which is likely caused by a larger fraction of field stars in our Hyades tails sample. Compared to previous studies, our sample is slightly fainter in X-rays due to differences in the Hyades membership list used; furthermore, we extend the X-ray luminosity distribution to fainter luminosities. The X-ray activity of F- and G-type stars is well defined at FX/Fbol ≈ 10−5. The fractional X-ray luminosity and its spread increases to later spectral types reaching the saturation limit (FX/Fbol ≈ 10−3) for members later than spectral type M3. Confirming previous results, the X-ray flux varies by less than a factor of three between epochs for the 104 Hyades members with multiple epoch data, significantly less than expected from solar-like activity cycles. Rotation periods are found for 204 Hyades members, with about half of them being detected in X-rays. The activity-rotation relation derived for the coeval Hyades members has properties very similar to those obtained by other authors investigating stars of different ages.

scholarly journals X-Ray Emission from Stellar Flares: Exosat Results

1989 ◽  
Vol 104 (2) ◽  
pp. 17-20 ◽  
Author(s):  
R. Pallavicini ◽  
G. Tagliaferri
Keyword(s):  
Main Sequence ◽  
Late Type ◽  
X Ray ◽  
Visual Binary ◽  
Stellar Flares ◽  
Flare Stars ◽  
M Dwarf

AbstractWe present an overview of recent observations of stellar X-ray flares obtained with the EXOSAT Observatory. We discuss a few examples of flares from M dwarf flare stars, from RS CVn and Algol-type binaries, from single late-type stars (including a G0 dwarf and an A-type visual binary), and from pre-main-sequence objects. We also draw some general conclusions from the pieliminary analysis of the EXOSAT data sample.

scholarly journals Activity and rotation of the X-ray emitting Kepler stars

2019 ◽  
Vol 628 ◽  
pp. A41 ◽  
Author(s):  
D. Pizzocaro ◽  
B. Stelzer ◽  
E. Poretti ◽  
S. Raetz ◽  
G. Micela ◽  
...  
Keyword(s):  
White Light ◽  
Main Sequence ◽  
Magnetic Activity ◽  
Light Curves ◽  
Late Type ◽  
Main Sequence Stars ◽  
Photometric Variability ◽  
X Ray ◽  
Rotation Periods ◽  
Flare Frequency

The relation between magnetic activity and rotation in late-type stars provides fundamental information on stellar dynamos and angular momentum evolution. Rotation-activity studies found in the literature suffer from inhomogeneity in the measurement of activity indexes and rotation periods. We overcome this limitation with a study of the X-ray emitting, late-type main-sequence stars observed by XMM-Newton and Kepler. We measured rotation periods from photometric variability in Kepler light curves. As activity indicators, we adopted the X-ray luminosity, the number frequency of white-light flares, the amplitude of the rotational photometric modulation, and the standard deviation in the Kepler light curves. The search for X-ray flares in the light curves provided by the EXTraS (Exploring the X-ray Transient and variable Sky) FP-7 project allows us to identify simultaneous X-ray and white-light flares. A careful selection of the X-ray sources in the Kepler field yields 102 main-sequence stars with spectral types from A to M. We find rotation periods for 74 X-ray emitting main-sequence stars, 20 of which do not have period reported in the previous literature. In the X-ray activity-rotation relation, we see evidence for the traditional distinction of a saturated and a correlated part, the latter presenting a continuous decrease in activity towards slower rotators. For the optical activity indicators the transition is abrupt and located at a period of ~10 d but it can be probed only marginally with this sample, which is biased towards fast rotators due to the X-ray selection. We observe seven bona-fide X-ray flares with evidence for a white-light counterpart in simultaneous Kepler data. We derive an X-ray flare frequency of ~0.15 d−1, consistent with the optical flare frequency obtained from the much longer Kepler time-series.

scholarly journals The X-ray stellar population of the LMC

2008 ◽  
Vol 4 (S256) ◽  
pp. 20-29 ◽  
Author(s):  
Yaël Nazé
Keyword(s):  
Stellar Population ◽  
Main Sequence ◽  
Massive Stars ◽  
High Energy ◽  
Magellanic Clouds ◽  
X Rays ◽  
X Ray ◽  
Energy Domain ◽  
X Ray Binaries

AbstractIn the study of stars, the high energy domain occupies a place of choice, since it is the only one able to directly probe the most violent phenomena: indeed, young pre-main sequence objects, hot massive stars, or X-ray binaries are best revealed in X-rays. However, previously available X-ray observatories often provided only crude information on individual objects in the Magellanic Clouds. The advent of the highly efficient X-ray facilities XMM-Newton and Chandra has now dramatically increased the sensitivity and the spatial resolution available to X-ray astronomers, thus enabling a fairly easy determination of the properties of individual sources in the LMC.

scholarly journals X-ray Flare Rate of T Tauri Stars in Taurus

1995 ◽  
Vol 151 ◽  
pp. 216-217
Author(s):  
R. Neuhäuser ◽  
Th. Preibisch
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
T Tauri Stars ◽  
Medium Size ◽  
Late Type ◽  
Large Sample ◽  
X Ray ◽  
T Tauri ◽  
Sky Survey ◽  
Low Mass

AbstractWe study the X-ray emission of several hundred (young, low-mass, late-type, pre-main sequence) T Tauri stars (TTS) in the Taurus T association, a nearby well-studied region of ongoing star formation. We report on X-ray emission variability of TTS as observed with the flux-limited ROSAT All-Sky Survey (RASS). Since RASS observations are spatially unbiased, we can investigate the X-ray flare rate of TTS on a large sample. We find that large flares are very rare (once per year), while medium-size flares can occur once in ∼ 40 days.

scholarly journals The Rotation of Pre-Main Sequence Stars

1980 ◽  
Vol 5 ◽  
pp. 835-837
Author(s):  
Leonard V. Kuhi ◽  
Stuart Vogel
Keyword(s):  
Angular Momentum ◽  
Spectral Type ◽  
Main Sequence ◽  
Rotational Velocity ◽  
The Sun ◽  
Main Sequence Stars ◽  
Lower Mass ◽  
B Stars ◽  
Large Numbers ◽  
Rapid Deceleration

Kraft (1970) obtained the rotational velocities for large numbers of stars located in the field and in clusters of different ages. He noted that (a) among the field stars those stars with strong Call K emission had larger rotational velocities than those without; (b) stars in the Hyades and Pleiades (which are much younger than the field) had both larger rotational velocities and stronger Call K emission than field stars; (c) there was a pronounced break at spectral type early F in v sini as a function of spectral type and (d) the distribution of angular momentum per unit, mass J(M⊚) was proportional to M0.57 for main sequence stars with mass M > 1.5 Mʘ. This distribution predicted a v sini of ˜75 km/sec for stars of lower mass (e.g. G type) but such high velocities were not seen in the Pleiades nor in the sun. This implied a more rapid deceleration of v sini for lower mass stars and led to estimates of the e-folding time of ˜4×l08 years for stars of 1.2 M⊚ to reduce their v sini from that of the Pleiades to that of the Hyades and ˜4×l09 years to go from the Hyades to the sun’s v sini. We note also that the age of the Pleiades is approximately equal to the pre-main sequence lifetime of a 1.0 M0 star so that the zero-age main sequence cannot have J(M) α M0.57 for ˜1 M0 stars. Skumanich (1972) showed that both the Call k emission and the rotational velocity decayed as the (age)-½ for main-sequence stars.

scholarly journals Foreign body in the heart muscle

1929 ◽  
Vol 25 (2) ◽  
pp. 230-230
Author(s):  
N. Vylegzhanin
Keyword(s):  
Foreign Body ◽  
Left Lung ◽  
Posterior Wall ◽  
Moderate Increase ◽  
X Rays ◽  
X Ray ◽  
Chest Cavity ◽  
The Third ◽  
Sixth Intercostal Space ◽  
Left Nipple

Hunter, Staub and Lunsford (Arch, of path. A. Lab. Med., Vol. 6, No. 5, 1928) observed a case when a patient with depressive-manic psychosis for the purpose of suicide introduced through the skin of the sixth intercostal space along the left nipple line an aluminum tube from the mouthpiece, 8.9 cm long, and 4 mm in diameter. Within two days, there were no subjective or objective symptoms, and only starting from the third day there was a moderate increase in temperature and an increase in pulse and respiration, which lasted until death, which occurred only on the 9th day, suddenly for 10 with the phenomena of sharp cyanosis , increased heart rate and respiration. An intravital X-ray examination did not reveal any foreign body in either the chest cavity or the heart. An autopsy showed that the tube passed over the apex of the heart through the wall of the left ventricle into its cavity and from there, through the posterior wall, entered into the left lung. There was a slight hemorrhage in the cardiac shirt and fresh fibrinous pericarditis. The authors explain the negative X-ray study by the light permeability of aluminum for all rays, with the exception of the shortest X-rays.

scholarly journals Activity and Rotation in the Young Cluster h Per

2013 ◽  
Vol 9 (S302) ◽  
pp. 102-105
Author(s):  
C. Argiroffi ◽  
M. Caramazza ◽  
G. Micela ◽  
E. Moraux ◽  
J. Bouvier
Keyword(s):  
Main Sequence ◽  
Activity Relationship ◽  
Central Field ◽  
Activity Levels ◽  
Rotational Period ◽  
Main Sequence Stars ◽  
Lower Mass ◽  
Significant Evidence ◽  
X Ray ◽  
Low Mass

AbstractWe study the rotation-activity relationship for low-mass members of the young cluster h Persei, a ~13 Myr old cluster. h Per, thanks to its age, allows us to link the rotation-activity relation observed for main-sequence stars to the still unexplained activity levels of very young clusters.We constrained the activity levels of h Per members by analyzing a deep Chandra/ACIS-I observation pointed to the central field of h Per. We combined this X-ray catalog with the catalog of h Per members with measured rotational period, presented by Moraux et al. (2013). We obtained a final catalog of 202 h Per members with measured X-ray luminosity and rotational period. We investigate the rotation-activity relation of h Per members considering different mass ranges. We find that stars with 1.3 M⊙ > M 1.4 M⊙ show significant evidence of supersaturation for short periods. This phenomenon is instead not observed for lower mass stars.

scholarly journals Protoplanetary disks and hard X-rays

2009 ◽  
Vol 5 (H15) ◽  
pp. 744-744
Author(s):  
Eric D. Feigelson ◽  
Philip J. Armitage ◽  
Konstantin V. Getman
Keyword(s):  
Magnetic Reconnection ◽  
Main Sequence ◽  
Protoplanetary Disks ◽  
X Rays ◽  
Physical Processes ◽  
Main Sequence Stars ◽  
Magnetorotational Instability ◽  
X Ray ◽  
Neutral Gas ◽  
Ionization Fraction

The physics of protoplanetary disks and the early stages of planet formation is strongly affected by the level of ionization of the largely-neutral gas (Armitage 2009; Balbus 2009). Where the ionization fraction is above some limit around ~ 10−12, the magnetorotational instability (MRI) will ensue and the gas will become turbulent. The presence or absence of disk turbulence at various locations and times has profound implications for viscosity, accretion, dust settling, protoplanet migration and other physical processes. The dominant source of ionization is very likely X-rays from the host star (Glassgold et al. 2000). X-ray emission is elevated in all pre-main sequence stars primarily due to the magnetic reconnection flares similar to, but much more powerful and frequent than, flares on the surface of the contemporary Sun (Feigelson et al. 2007).

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