Explore the vast range of titles available.

ABSTRACT In this article we report the discovery of the chromospherically active (RS CVn type) binary TYC 8380-1953-1 through the XMM-Newton slew survey and present results of our optical and X-ray follow-up. With a flux limit of 6 × 10-13 ergs cm-2 s-1 in the soft band (0.2-2 keV), the XMM-Newton slew has a similar sensitivity to the ROSAT All Sky Survey, allowing interesting sources to be identified by their long-term variability. Two different types of stellar sources are detected in shallow X-ray surveys: young stars (both pre-main- and main-sequence stars) and chromospherically active binaries (BY Dra and RS CVn-type systems). The discovery of stars in such surveys and the study of their nature through optical follow-ups is valuable to determine their spatial distribution and scale height in the Galaxy. Our analysis shows that TYC 8380-1953-1 is a double-lined spectroscopic binary, with both components having similar spectral type (likely K0/2 + K3/5) and luminosity. With a typical coronal temperature for an RS CVn system (kT ∼ 1.15 keV) and an X-ray luminosity in the 0.3-10 keV energy band higher than 4 × 1031 erg s-1, TYC 8380-1953-1 lies among the most X-ray luminous RS CVn binaries.

We present new photometric and spectroscopic data for the M-type members of the TW Hya association with the aim of a comprehensive study of accretion, disks and magnetic activity at the critical age of ~ 10 Myr where circumstellar matter disappears.

We present the first study of nearby M dwarfs with the ROentgen Survey with an Imaging Telescope Array (eROSITA) on board the Russian Spektrum-Roentgen-Gamma mission (SRG). To this end we extracted the Gaia DR2 data for the ~9000 nearby M dwarfs in the superblink proper motion catalog and calculated their stellar parameters from empirical relations with optical-IR colors. We cross-matched this catalog with the eROSITA Final Equatorial Depth Survey (eFEDS) and the first eROSITA all-sky survey (eRASS1). Our sample consists of 704 stars (SpT = K5-M7). This unprecedented data base for X-ray emitting M dwarfs allowed to quantitatively constrain the mass dependence of the X-ray luminosity, and to determine the change in the activity level with respect to pre-main-sequence stars. We also combined these data with the Transiting Exoplanet Survey Satellite (TESS) observations that are available for 501 of 704 X-ray detected M dwarfs and determined the rotation period for 180 of them. With the joint eROSITA-TESS sample, and combining it with our historical X-ray and rotation data for M dwarfs, we examined the mass dependence in the saturated regime of the rotation-activity relation. A first comparison of eROSITA hardness ratios and spectra shows that 65% of our X-ray detected M dwarfs have coronal temperatures of \\(\\sim 0.5\\) keV. We investigated their long-term X-ray variability by comparing the eRASS1 and ROSAT all-sky survey (RASS) measurements. Evidence for X-ray flares is found in various parts of our analysis: directly from inspection of the eFEDS light curves, in the relation between RASS and eRASS1 X-ray luminosities, and in stars displaying X-ray emission hotter than the bulk of the sample according to the hardness ratios. Finally, we point out the need of X-ray spectroscopy for more M dwarfs to study the coronal temperature-luminosity relation, not well constrained by our eFEDS results.

In this article we report the discovery of the chromospherically active (RS CVn type) binary TYC 8380-1953-1 through theXMM-Newtonslew survey and present results of our optical and X-ray follow-up. With a flux limit of6 × 10-13 ergs cm-2 s-1 6 × 10 - 13     ergs   cm - 2   s - 1 in the soft band (0.2–2 keV), theXMM-Newtonslew has a similar sensitivity to theROSATAll Sky Survey, allowing interesting sources to be identified by their long-term variability. Two different types of stellar sources are detected in shallow X-ray surveys: young stars (both pre–main- and main-sequence stars) and chromospherically active binaries (BY Dra and RS CVn-type systems). The discovery of stars in such surveys and the study of their nature through optical follow-ups is valuable to determine their spatial distribution and scale height in the Galaxy. Our analysis shows that TYC 8380-1953-1 is a double-lined spectroscopic binary, with both components having similar spectral type (likelyK0/2 + K3/5 K 0 / 2 + K 3 / 5 ) and luminosity. With a typical coronal temperature for an RS CVn system ( kT ∼ 1.15 keV k T ∼ 1.15     keV ) and an X-ray luminosity in the 0.3–10 keV energy band higher than4 × 1031 erg s-1 4 × 10 31     erg   s - 1 , TYC 8380-1953-1 lies among the most X-ray luminous RS CVn binaries.

Studies of the rotation and activity of M type stars are essential to enhance our understanding of stellar dynamos and angular momentum evolution. Using the outstanding photometric capabilities of space telescopes rotation signals even with low amplitudes can be investigated in up to now unrivaled detail. By combining data of K2 and the TESS prime mission the star spot activity of M dwarfs can be monitored on half a decade timescale. In the framework of our study on the rotation-activity relation for bright and nearby M dwarfs we also aim at an investigation of the long-term activity. While K2 was observing fields distributed around the ecliptic plane, the TESS prime mission was oriented along a line of ecliptic longitude with one camera centered on an ecliptic pole. Due to these different observing strategies, the overlap between K2 and the TESS prime mission is marginal. However, 45 stars from our sample were observed with both missions of which two early M-type stars that fulfill our selection criteria, EPIC 202059229 and EPIC 245919787, were analyzed in more detail. We found that for both stars the rotation period did not change while the rotational phase did change for EPIC 245919787 by ~0.2. The amplitude of the spot induced variability changed for both stars but more significant for EPIC 245919787. By comparing the cumulative flare frequency distributions we found that the flare activity for EPIC 202059229 is unchanged while it slightly changes for EPIC 245919787 between the K2 and TESS epochs. Using a combination of light curves from K2 and TESS that span a baseline up to 4.5 years we could measure significant differential rotation for EPIC 245919787. Furthermore, we show that combining missions like K2 and TESS is a promising method for detecting stellar activity cycles.

The nearest, youngest groups of stars to the Sun provide important samples of age-dated stars for studying circumstellar disk evolution, imaged exoplanets, and brown dwarfs. I briefly comment on the status of the known stellar groups within 100 pc: β Pic, AB Dor, UMa, Car-Near, Tuc-Hor and β Tuc nucleus, Hyades, Col, TW Hya, Car, Coma Ber, 32 Ori, η Cha, and χ1 For. I also discuss some poorly characterized groups and “non-groups.” Grades for 2015 of Pass, Satisfactory, or Fail are assigned to the groups for the purposes of age-dating stars and brown dwarfs. I speculate that Tuc-Hor could have provided a supernova ~60 pc away ~2.2 Myr ago which showered the Earth with traces of 60Fe-bearing dust.

The λ Orionis star formation region (1-6 Myr, 400 pc) is a complex of star-forming clouds surrounded by a molecular ring with ~ 5° radius which was probably formed by a supernova explosion (Dolan & Mathieu 2002). For a complete picture of star formation, believed to be determined by the supernova blast, the large-scale distribution of the pre-main sequence population in λ Ori needs to be examined. We have embarked on a multi-wavelength study (XMM-Newton/X-ray, CFHT/optical, Spitzer/IR) of selected areas within this intriguing star-forming complex that enables us to identify young stars and brown dwarfs. Our study comprises various areas within the cloud complex as shown in Fig.1. This data set is among the most extended X-ray surveys carried out with XMM-Newton in a coherent star-forming environment. The XMM-Newton observations combined with optical and IR data reveal the low-mass stellar population down to ~ 0.4 M⊙. For this mass-limited sample, our preliminary analysis confirms the anomalously low disk-fraction of the central star cluster Coll 69, the Eastern extension of its low-mass population pointing towards B 35, and the concentration of young stars in front of B 35. The analysis of the ‘on-cloud field' of B 35 (white in the figure) will show if the cloud is currently forming stars. This will be crucial for determining the star-forming history in the whole λ Ori region.

We present the results of a new magnetic field survey of Herbig Ae/Be and A debris disk stars. They are used to determine whether magnetic field properties in these stars are correlated with the mass-accretion rate, disk inclinations, companion(s), Silicates, PAHs, or show a more general correlation with age and X-ray emission as expected for the decay of a remnant dynamo.

I present the first substantial work to measure the fraction of debris disks for M-dwarfs in nearby moving groups (MGs). Utilising the AllWISE IR catalog, 17 out of 151 MG members are found with an IR photometric excess indicative of disk structure. The M-dwarf debris disk fraction is ≲6 per cent in MGs younger than 40 Myr, and none are found in the groups older than 40 Myr. Simulations show, however, that debris disks around M-dwarfs are not present above a WISEW1-W4 colour of ~2.5, making calculating the absolute disk fractions difficult. The debris disk dissipation timescale appears to be faster than for higher-mass stars, and mechanisms such as enhanced stellar wind drag and/or photoevaporation could account for the more rapid decline of disks observed amongst M-dwarfs.

We highlight differences in spectral types and intrinsic colors observed in pre-main sequence (pre-MS) stars. Spectral types of pre-MS stars are wavelength-dependent, with near-infrared spectra being 3-5 spectral sub-classes later than the spectral types determined from optical spectra. In addition, the intrinsic colors of young stars differ from that of main-sequence stars at a given spectral type. We caution observers to adopt optical spectral types over near-infrared types, since Hertzsprung-Russell (H-R) diagram positions derived from optical spectral types provide consistency between dynamical masses and theoretical evolutionary tracks. We also urge observers to deredden pre-MS stars with tabulations of intrinsic colors specifically constructed for young stars, since their unreddened colors differ from that of main sequence dwarfs. Otherwise, V-band extinctions as much as ~0.6 mag erroneously higher than the true extinction may result, which would introduce systematic errors in the H-R diagram positions and thus bias the inferred ages.