scholarly journals Simultaneous eROSITA and TESS observations of the ultra-active star AB Doradus

2021 ◽  
Author(s):  
J. H. H. M. Schmitt ◽  
P. Ioannidis ◽  
J. Robrade ◽  
P. Predehl ◽  
S. Czesla ◽  
...  
Keyword(s):  
Active Star

scholarly journals MOST Spacebased Photometry of HD 189733: Precise Timing Measurements for Transits Across an Active Star

2008 ◽  
Vol 4 (S253) ◽  
pp. 459-461
Author(s):  
E. Miller-Ricci ◽  
J. F. Rowe ◽  
D. Sasselov ◽  
J. M. Matthews ◽  
R. Kuschnig ◽  
...  
Keyword(s):  
Orbital Period ◽  
Mass Range ◽  
Active Star ◽  
Precise Timing ◽  
Resonant Orbits ◽  
The Earth ◽  
Test Spot ◽  
Transit Times ◽  
Nearly Continuous ◽  
Parent Star

AbstractWe have measured transit times for HD 189733 passing in front of its bright (V = 7.67) chromospherically active and spotted parent star. Nearly continuous broadband photometry of this system was obtained with the MOST (Microvariability & Oscillations of STars) space telesope during 21 days in August 2006, monitoring 10 consecutive transits. We have used these data to search for deviations from a constant orbital period which can indicate the presence of additional planets in the system that are as yet undetected by Doppler searches. We find no variations above the level of ±45 s, ruling out planets in the Earth-to-Neptune mass range in a number of resonant orbits. We find that a number of complications can arise in measuring transit times for a planet transiting an active star with large star spots. However, such transiting systems are also useful in that they can help to constrain and test spot models. This has implications for the large number of transiting systems expected to be discovered by the CoRoT and Kepler missions.

scholarly journals KIC 2557430: A Triple System Containing One γ Dor and Two Flaring Components?

2017 ◽  
Vol 34 ◽  
Author(s):  
Ceren Kamil ◽  
Hasan Ali Dal
Keyword(s):  
Triple System ◽  
Primary Component ◽  
Mass Ratio ◽  
Third Body ◽  
Period Analysis ◽  
Active Star ◽  
Group 2 ◽  
Different Sources ◽  
Flare Frequency ◽  
Group 1

AbstractThe results are presented for eclipsing binary KIC 2557430. The mass ratio was computed as 0.868 ± 0.002, while the inclination (i) was found as 69°.75 ± 0°.01 with T2 = 6271±1 K. 50 frequencies were found in the period analysis. 48 frequencies of them are caused due to the primary component, a γ Doradus star, while two of them are caused by the cool spots. 69 flares were detected in the analyses. Two OPEA models were derived for flares, which indicates that the flares were come from two different sources. The Plateau value was found to be 1.4336 ± 0.1104 s for Source 1, which is seen as possible the secondary component and 0.7550 ± 0.0677 s for Source 2, which is seen as possible third body. The half-life value was computed as 2278.1 s for Group 1 and 1811.2 s for Group 2. The flare frequency N1 was found to be 0.02726 h−1 and N2 was computed as 0.00002 for Group 1, while N1 was found to be 0.01977 h−1 and N2 was computed as 0.00001 for Group 2. In a results, KIC 2557430 is a possible triple system consisting of a γ Doradus-type star, a chromospherically active star, and also a flaring third body.

scholarly journals The global star formation law: from dense cores to extreme starbursts

2006 ◽  
Vol 2 (S237) ◽  
pp. 331-335
Author(s):  
Yu Gao
Keyword(s):  
Star Formation ◽  
Linear Correlation ◽  
Molecular Clouds ◽  
High Redshift ◽  
Gas Content ◽  
Molecular Gas ◽  
Giant Molecular Clouds ◽  
Active Star ◽  
Dense Cores ◽  
The Galaxy

AbstractActive star formation (SF) is tightly related to the dense molecular gas in the giant molecular clouds' dense cores. Our HCN (measure of the dense molecular gas) survey in 65 galaxies (including 10 ultraluminous galaxies) reveals a tight linear correlation between HCN and IR (SF rate) luminosities, whereas the correlation between IR and CO (measure of the total molecular gas) luminosities is nonlinear. This suggests that the global SF rate depends more intimately upon the amount of dense molecular gas than the total molecular gas content. This linear relationship extends to both the dense cores in the Galaxy and the hyperluminous extreme starbursts at high-redshift. Therefore, the global SF law in dense gas appears to be linear all the way from dense cores to extreme starbursts, spanning over nine orders of magnitude in IR luminosity.

scholarly journals A Highly Active Star Decahedron Cu Nanocatalyst for Hydrocarbon Production at Low Overpotentials

2018 ◽  
pp. 1805405 ◽  
Author(s):  
Chungseok Choi ◽  
Tao Cheng ◽  
Michelle Flores Espinosa ◽  
Huilong Fei ◽  
Xiangfeng Duan ◽  
...  
Keyword(s):  
Hydrocarbon Production ◽  
Active Star ◽  
Highly Active

scholarly journals Flare-Like Events on the T-Tauri Star RU LUP1

1989 ◽  
Vol 104 (2) ◽  
pp. 139-142 ◽  
Author(s):  
F. Giovannelli ◽  
D. Castaldo ◽  
E. Covino ◽  
A.A. Vittone ◽  
C. Rossi
Keyword(s):  
Tauri Star ◽  
Quiescent State ◽  
Complete Coverage ◽  
Patchy Distribution ◽  
Active Star ◽  
X Ray ◽  
T Tauri ◽  
Observed Behaviour ◽  
Flare Stars

AbstractA long term multifrequency campaign on the T Tauri star RU Lupi has been carried out in the X-Ray, UV optical and IR spectral regions with ASTRON and IUE satellites and ESO 1.5 m+IDS, 1.4 m CAT, 0.5 m UBVRI and 1 m IR telescopes, respectively.We present two flare-like events occurred on April 17, 1984 and June 30, 1986. The first one was detected only in the UV, clue to lack the of simultaneous observations in other spectral regions. The second one was observed in UV, optical and IR regions showing a maximum roughly in the U band A comparison of the whole energy distribution of this event with that of a quiescent state observed on June 27 shows a flux enhancement of (89 ± 2)%. A detailed analysis of UV continuum and lines, namely N V, C I, CII, CIV, Si II and Si IV, shows that ihe surfaces fluxes of RU Lupi are always larger than those observed on typical flare stars and on the Sun by a factor of roughly 2 and 3 orders of magnitude, respectively. This fact allows us to conclude that RU Lupi activity cannot be explained even invoking a complete coverage by solar-like plages. On the contrary a patchy distribution of the emitting regions could explain the observed behaviour of this active star.

scholarly journals Small Galactic Nebulae

1987 ◽  
Vol 115 ◽  
pp. 191-192
Author(s):  
Yervant Terzian ◽  
Kenneth C. Turner
Keyword(s):  
High Resolution ◽  
Planetary Nebula ◽  
Physical Parameters ◽  
H Ii Regions ◽  
Radio Observations ◽  
Cluster Emission ◽  
Active Star ◽  
Star Forming ◽  
Cometary Nebula ◽  
Significant Flux

We have performed high resolution VLA radio observations for several small H II regions, including the cluster emission nebulae S258, S255, S257, and S256. The region (PP56) between S255 and S257 at λ2 cm reveals significant flux structure close to OH, H2O and infrared emitting sources as shown in Figure 1. The flux densities and positions are indicated in Table 1. Observations of the cometary nebula PP59 (S269) also reveal similar characteristics as shown in Figure 2. These regions are considered to be active star-forming clouds. The cometary nebula PP40 was also observed and we note that its physical parameters are very similar to those of a typical planetary nebula.

scholarly journals Star Formation Thresholds in Low Surface Brightness Dwarf Galaxies

1999 ◽  
Vol 171 ◽  
pp. 274-281
Author(s):  
Liese van Zee
Keyword(s):  
Star Formation ◽  
Comparative Study ◽  
Column Density ◽  
Surface Brightness ◽  
Dwarf Galaxies ◽  
Critical Threshold ◽  
Active Star ◽  
Comparison Sample ◽  
Active Star Formation ◽  
Low Surface Brightness

AbstractThe results of a comparative study of star formation thresholds in gas-rich, low surface brightness, dwarf galaxies are presented. Approximately half the galaxies in the study were “high MH/LB” galaxies, which appear to have inefficient star formation properties. The comparison sample comprised of otherwise “normal” dwarf galaxies, with moderate current star formation rates. In all systems, sites of active star formation were associated with local peaks in the HI column density. For both types of galaxies, the azimuthally averaged gas column density is low. Similar to other LSB systems, the global gas densities are well below the critical threshold for star formation throughout the system. Thus, star formation is inhibited globally, but occurs locally in these gas-rich dwarf galaxies.

scholarly journals Lithium Abundance and Spacial Distribution of T Tauri Stars

1992 ◽  
Vol 150 ◽  
pp. 395-397
Author(s):  
Jane Gregorio-Hetem ◽  
Jacques R.D. Lépine
Keyword(s):  
Star Formation ◽  
Equivalent Width ◽  
Molecular Cloud ◽  
Resonance Line ◽  
T Tauri Stars ◽  
Lithium Abundance ◽  
Active Star ◽  
T Tauri ◽  
Star Formation Regions ◽  
Line Equivalent Width

We determined temperatures and Lithium 6707 A resonance line equivalent width of a sample of 62 T Tauri stars. Lithium abundances were then estimated by using a grid of curves of growth. The lithium abundance is shown to decrease with the distance of the stars to the nearest dense core of a molecular cloud. This effect is interpreted as being due to the ages of the stars, the youngest ones being closer to still active star formation regions.

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