scholarly journals A kinematically unbiased, all-sky search for nearby, young, low-mass stars

2019 ◽  
Vol 491 (1) ◽  
pp. 215-234 ◽  
Author(s):  
Alexander S Binks ◽  
Matthieu Chalifour ◽  
Joel H Kastner ◽  
David Rodriguez ◽  
Simon J Murphy ◽  
...  
Keyword(s):  
Young Star ◽  
Photometric Data ◽  
Young Stars ◽  
Stellar Clusters ◽  
Late Type ◽  
Low Mass Stars ◽  
Near Ir ◽  
Field Star ◽  
Low Mass ◽  
Moving Groups

ABSTRACT The past two decades have seen dramatic progress in our knowledge of the population of young stars of age $\lt \!200\,$ Myr that lie within $150\,$ pc of the Sun. These nearby, young stars, most of which are found in loose, comoving groups, provide the opportunity to explore (among many other things) the dissolution of stellar clusters and their diffusion into the field star population. Here, we exploit the combination of astrometric and photometric data from Gaia and photometric data from GALEX (UV) and 2MASS (near-IR) in an attempt to identify additional nearby, young, late-type stars. Specifically, we present a sample of 146 GALEX UV-selected late-type (predominantly K-type) field stars with Gaia-based distances $\lt \!125\,$ pc (based on Gaia Data Release 1) that have isochronal ages $\lt \!80\,$ Myr even if equal-components binaries. We investigate the spectroscopic and kinematic properties of this sample. Despite their young isochronal ages, only ∼10 per cent of stars among this sample can be confidently associated with established nearby, young moving groups (MGs). These candidate MG members include five stars newly identified in this study. The vast majority of our sample of 146 nearby young star candidates have anomalous kinematics relative to the known MGs. These stars may hence represent a previously unrecognized population of young stars that has recently mixed into the older field star population. We discuss the implications and caveats of such a hypothesis – including the intriguing fact that, in addition to their non-young-star-like kinematics, the majority of the UV-selected, isochronally young field stars within $50\,$ pc appear surprisingly X-ray faint.

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.

scholarly journals BANYAN. V. A SYSTEMATIC ALL-SKY SURVEY FOR NEW VERY LATE-TYPE LOW-MASS STARS AND BROWN DWARFS IN NEARBY YOUNG MOVING GROUPS

2014 ◽  
Vol 798 (2) ◽  
pp. 73 ◽  
Author(s):  
Jonathan Gagné ◽  
David Lafrenière ◽  
René Doyon ◽  
Lison Malo ◽  
Étienne Artigau
Keyword(s):  
Brown Dwarfs ◽  
Late Type ◽  
Low Mass Stars ◽  
Sky Survey ◽  
Low Mass ◽  
Moving Groups

scholarly journals The effect of photoionizing feedback on the shaping of hierarchically-forming stellar clusters

2020 ◽  
Vol 499 (1) ◽  
pp. 668-680
Author(s):  
Alejandro González-Samaniego ◽  
Enrique Vazquez-Semadeni
Keyword(s):  
Star Formation ◽  
Early Stage ◽  
Stellar Clusters ◽  
Low Mass Stars ◽  
Transfer Scheme ◽  
Star Forming ◽  
Secondary Star ◽  
Low Mass ◽  
Hydrodynamical Simulations ◽  
Formation Efficiency

ABSTRACT We use two hydrodynamical simulations (with and without photoionizing feedback) of the self-consistent evolution of molecular clouds (MCs) undergoing global hierarchical collapse (GHC), to study the effect of the feedback on the structural and kinematic properties of the gas and the stellar clusters formed in the clouds. During this early stage, the evolution of the two simulations is very similar (implying that the feedback from low-mass stars does not affect the cloud-scale evolution significantly) and the star-forming region accretes faster than it can convert gas into stars, causing the instantaneous measured star formation efficiency (SFE) to remain low even in the absence of significant feedback. Afterwards, the ionizing feedback first destroys the filamentary supply to star-forming hubs and ultimately removes the gas from it, thus first reducing the star formation (SF) and finally halting it. The ionizing feedback also affects the initial kinematics and spatial distribution of the forming stars because the gas being dispersed continues to form stars, which inherit its motion. In the non-feedback simulation, the groups remain highly compact and do not mix, while in the run with feedback, the gas dispersal causes each group to expand, and the cluster expansion thus consists of the combined expansion of the groups. Most secondary star-forming sites around the main hub are also present in the non-feedback run, implying a primordial rather than triggered nature. We do find one example of a peripheral star-forming site that appears only in the feedback run, thus having a triggered origin. However, this appears to be the exception rather than the rule, although this may be an artefact of our simplified radiative transfer scheme.

scholarly journals Giant planets around AF and M stars

2013 ◽  
Vol 8 (S299) ◽  
pp. 64-65
Author(s):  
Julien Rameau ◽  
Gaël Chauvin ◽  
Anne-Marie Lagrange ◽  
Philippe Delorme ◽  
Justine Lannier
Keyword(s):  
Giant Planets ◽  
Early Type ◽  
Late Type ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
Planetary Mass ◽  
Nearby Stars ◽  
Low Mass ◽  
M Stars ◽  
The One

AbstractWe present the results of two three-year surveys of young and nearby stars to search for wide orbit giant planets. On the one hand, we focus on early-type and massive, namely β Pictoris analogs. On the other hand, we observe late type and very low mass stars, i.e., M dwarfs. We report individual detections of new planetary mass objects. According to our deep detection performances, we derive the observed frequency of giant planets between these two classes of parent stars. We find frequency between 6 to 12% but we are not able to assess a/no correlation with the host-mass.

scholarly journals A kinematically hot population of young stars in the solar neighbourhood

2020 ◽  
Vol 494 (2) ◽  
pp. 2429-2439 ◽  
Author(s):  
A S Binks ◽  
R D Jeffries ◽  
N J Wright
Keyword(s):  
Young Stars ◽  
Solar Neighbourhood ◽  
Mass Distributions ◽  
Systematic Effort ◽  
Low Mass ◽  
Moving Groups

ABSTRACT In the last three decades several hundred nearby members of young stellar moving groups (MGs) have been identified, but there has been less systematic effort to quantify or characterize young stars that do not belong to previously identified MGs. Using a kinematically unbiased sample of 225 lithium-rich stars within 100 pc, we find that only 50 ± 10 per cent of young (≲125 Myr), low-mass (0.5 < M/M⊙ < 1.0) stars, are kinematically associated with known MGs. Whilst we find some evidence that five of the non-MG stars may be connected with the Lower Centaurus–Crux association, the rest form a kinematically ‘hotter’ population, much more broadly dispersed in velocity, and with no obvious concentrations in space. The mass distributions of the MG members and non-MG stars are similar, but the non-MG stars may be older on average. We briefly discuss several explanations for the origin of the non-MG population.

scholarly journals The CARMENES search for exoplanets around M dwarfs

2018 ◽  
Vol 620 ◽  
pp. A171 ◽  
Author(s):  
R. Luque ◽  
G. Nowak ◽  
E. Pallé ◽  
D. Kossakowski ◽  
T. Trifonov ◽  
...  
Keyword(s):  
Bimodal Distribution ◽  
Photometric Data ◽  
M Dwarfs ◽  
Visual Channel ◽  
Low Mass Stars ◽  
Short Period ◽  
Low Mass ◽  
Periodic Signals ◽  
M Stars ◽  
Host Stars

We announce the discovery of two planetary companions orbiting around the low-mass stars Ross 1020 (GJ 3779, M4.0V) and LP 819-052 (GJ 1265, M4.5V). The discovery is based on the analysis of CARMENES radial velocity (RV) observations in the visual channel as part of its survey for exoplanets around M dwarfs. In the case of GJ 1265, CARMENES observations were complemented with publicly available Doppler measurements from HARPS. The datasets reveal two planetary companions, one for each star, that share very similar properties: minimum masses of 8.0 ± 0.5 M⊕ and 7.4 ± 0.5 M⊕ in low-eccentricity orbits with periods of 3.023 ± 0.001 d and 3.651 ± 0.001 d for GJ 3779 b and GJ 1265 b, respectively. The periodic signals around 3 d found in the RV data have no counterpart in any spectral activity indicator. Furthermore, we collected available photometric data for the two host stars, which confirm that the additional Doppler variations found at periods of approximately 95 d can be attributed to the rotation of the stars. The addition of these planets to a mass-period diagram of known planets around M dwarfs suggests a bimodal distribution with a lack of short-period low-mass planets in the range of 2–5 M⊕. It also indicates that super-Earths (>5 M⊕) currently detected by RV and transit techniques around M stars are usually found in systems dominated by a single planet.

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 PLANETS AROUND LOW-MASS STARS (PALMS). V. AGE-DATING LOW-MASS COMPANIONS TO MEMBERS AND INTERLOPERS OF YOUNG MOVING GROUPS

2015 ◽  
Vol 806 (1) ◽  
pp. 62 ◽  
Author(s):  
Brendan P. Bowler ◽  
Evgenya L. Shkolnik ◽  
Michael C. Liu ◽  
Joshua E. Schlieder ◽  
Andrew W. Mann ◽  
...  
Keyword(s):  
Age Dating ◽  
Low Mass Stars ◽  
Low Mass ◽  
Moving Groups

scholarly journals A Pan-STARRS1 Search for Substellar Young Moving Group Members

2015 ◽  
Vol 10 (S314) ◽  
pp. 54-57
Author(s):  
Kimberly M. Aller ◽  
Michael C. Liu ◽  
Eugene A. Magnier
Keyword(s):  
Large Scale ◽  
Spectral Characteristics ◽  
Mass Function ◽  
Initial Mass Function ◽  
Valuable Insight ◽  
Near Ir ◽  
Group Members ◽  
Low Mass ◽  
Moving Groups ◽  
Ir Photometry

AbstractYoung moving groups (YMGs) are coeval, comoving groups of stars which have migrated from their birthsites after formation. In the substellar regime, YMG members are key benchmarks to empirically define brown dwarf evolution with age and to study the lowest mass end of the initial mass function. We have combined Pan-STARRS1 (PS1) proper motions with optical+IR photometry from PS1, 2MASS and WISE to perform a large-scale (≈30,000 deg2) systematic search for substellar members down to ≈10 MJup. We have obtained near-IR spectroscopy of a large sample of ultracool candidate YMG members to assess their youth via gravity-sensitive absorption features. We have identified several new intermediate-gravity candidate members of the AB Dor Moving Group, potentially greatly expanding the substellar membership. These new candidate members bridge the gap between the known low-mass stellar and planetary-mass members and yield valuable insight into the spectral characteristics of young brown dwarfs.

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