scholarly journals Planetary candidates transiting cool dwarf stars from campaigns 12 to 15 of K2

2020 ◽  
Vol 499 (4) ◽  
pp. 5416-5441
Author(s):  
A Castro González ◽  
E Díez Alonso ◽  
J Menéndez Blanco ◽  
John H Livingston ◽  
Jerome P de Leon ◽  
...  
Keyword(s):  
False Positive ◽  
Habitable Zone ◽  
Positive Probability ◽  
Low Mass Stars ◽  
Dwarf Stars ◽  
Cool Stars ◽  
Nearby Stars ◽  
Low Mass ◽  
False Positive Probability ◽  
Gaia Dr2

ABSTRACT We analysed the photometry of 20 038 cool stars from campaigns 12, 13, 14, and 15 of the K2 mission in order to detect, characterize, and validate new planetary candidates transiting low-mass stars. We present a catalogue of 25 new periodic transit-like signals in 22 stars, of which we computed the parameters of the stellar host for 19 stars and the planetary parameters for 21 signals. We acquired speckle and AO images, and also inspected archival Pan-STARRS1 images and Gaia DR2 to discard the presence of close stellar companions and to check possible transit dilutions due to nearby stars. False positive probability (FPP) was computed for 22 signals, obtaining FPP < $1{{\ \rm per\ cent}}$ for 17. We consider 12 of them as statistically validated planets. One signal is a false positive and the remaining 12 signals are considered as planet candidates. 20 signals have an orbital period of P$_{\rm orb} \lt 10\,\mathrm{ d}$, 2 have $10\, \mathrm{ d} \lt $  P$_{\rm orb} \lt 20\, \mathrm{ d}$, and 3 have P$_{\rm orb} \gt 20\, \mathrm{ d}$. Regarding radii, 11 candidates and validated planets have computed radius R < 2R⊕, 9 have 2R⊕ < R < 4R⊕, and 1 has R > 4R⊕. Two validated planets and two candidates are located in moderately bright stars ($\rm \mathit{ m}_{kep}\lt 13$) and two validated planets and three candidates have derived orbital radius within the habitable zone according to optimistic models. Of special interest is the validated warm super-Earth K2-323 b (EPIC 248616368 b) with T$_{\rm eq} = 318^{+24}_{-43} \, \mathrm{ K}$, S$_{\rm p} = 1.7\pm 0.2 \, \mathrm{ S}_{\oplus }$, and R$_{\rm p} = 2.1\pm 0.1 \, \mathrm{ R}_{\oplus }$, located in an m$\rm _{kep}$ = 14.13 star.

scholarly journals Twenty years of photometric microlensing events predicted by Gaia DR2

2018 ◽  
Vol 617 ◽  
pp. A135 ◽  
Author(s):  
Alexander J. Mustill ◽  
Melvyn B. Davies ◽  
Lennart Lindegren
Keyword(s):  
Habitable Zone ◽  
Proper Motions ◽  
Low Mass Stars ◽  
Habitable Zones ◽  
Future Events ◽  
Low Mass ◽  
Effective Temperatures ◽  
Two Parameter ◽  
Gaia Dr2 ◽  
Background Star

Context. Gaia Data Release 2 (DR2) offers unparalleled precision on stars’ parallaxes and proper motions. This allows the prediction of microlensing events for which the lens stars (and any planets they possess) are nearby and may be well studied and characterised. Aims. We identify a number of potential microlensing events that will occur before the year 2035.5, 20 years from the Gaia DR2 reference epoch. Methods. We query Gaia DR2 for potential lenses within 100 pc, extract parallaxes and proper motions of the lenses and background sources, and identify potential lensing events. We estimate the lens masses from Priam effective temperatures and use these to calculate peak magnifications and the size of the Einstein radii relative to the lens stars’ habitable zones. Results. We identify seven future events with a probability >10% of an alignment within one Einstein radius. Of particular interest is DR2 5918299904067162240 (WISE J175839.20–583931.6), magnitude G = 14.9, which will lens a G = 13.9 background star in early 2030, with a median 23% net magnification. Other pairs are typically fainter, hampering characterisation of the lens (if the lens is faint) or the ability to accurately measure the magnification (if the source is much fainter than the lens). Of timely interest is DR2 4116504399886241792 (2MASS J17392440–2327071), which will lens a background star in July 2020, albeit with weak net magnification (0.03%). Median magnifications for the other five high-probability events range from 0.3% to 5.3%. The Einstein radii for these lenses are one to ten times the radius of the habitable zone, allowing these lensing events to pick out cold planets around the ice line, and filling a gap between transit and current microlensing detections of planets around very low-mass stars. Conclusions. We provide a catalogue of the predicted events to aid future characterisation efforts. Current limitations include a lack of many high-proper-motion objects in Gaia DR2 and often large uncertainties on the proper motions of the background sources (or only two-parameter solutions). Both of these deficiencies will be rectified with Gaia DR3 in 2020. Further characterisation of the lenses is also warranted to better constrain their masses and predict the photometric magnifications.

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 The rotation of low mass stars at 30 Myr in the cluster NGC 3766

2019 ◽  
Vol 15 (S354) ◽  
pp. 200-203
Author(s):  
Julia Roquette ◽  
Jerome Bouvier ◽  
Estelle Moraux ◽  
Herve Bouy ◽  
Jonathan Irwin ◽  
...  
Keyword(s):  
Wide Field ◽  
Stellar Rotation ◽  
Low Mass Stars ◽  
Photometric Variability ◽  
Direct Measurements ◽  
Active Stars ◽  
Low Mass ◽  
Gaia Dr2

AbstractTogether with the stellar rotation, the spotted surfaces of low-mass magnetically active stars produce modulations in their brightness. These modulations can be resolved by photometric variability surveys, allowing direct measurements of stellar spin rates. In this proceedings, we present results of a multisite photometric survey dedicated to the measurement of spin rates in the 30 Myr cluster NGC 3766. Inside the framework of the Monitor Project, the cluster was monitored during 2014 in the i-band by the Wide Field Imager at the MPG/ESO 2.2-m telescope. Data from Gaia-DR2 and grizY photometry from DECam/CTIO were used to identify cluster members. We present spin rates measured for ⁓200 cluster members.

scholarly journals Erosion of an exoplanetary atmosphere caused by stellar winds

2019 ◽  
Vol 630 ◽  
pp. A52 ◽  
Author(s):  
J. M. Rodríguez-Mozos ◽  
A. Moya
Keyword(s):  
Stellar Wind ◽  
Extreme Environment ◽  
Stellar Winds ◽  
Habitable Zone ◽  
Low Mass Stars ◽  
Zone Versus ◽  
Low Mass ◽  
The Difference ◽  
Interaction Regions ◽  
The Impact

Aims. We present a formalism for a first-order estimation of the magnetosphere radius of exoplanets orbiting stars in the range from 0.08 to 1.3 M⊙. With this radius, we estimate the atmospheric surface that is not protected from stellar winds. We have analyzed this unprotected surface for the most extreme environment for exoplanets: GKM-type and very low-mass stars at the two limits of the habitable zone. The estimated unprotected surface makes it possible to define a likelihood for an exoplanet to retain its atmosphere. This function can be incorporated into the new habitability index SEPHI. Methods. Using different formulations in the literature in addition to stellar and exoplanet physical characteristics, we estimated the stellar magnetic induction, the main characteristics of the stellar wind, and the different star-planet interaction regions (sub- and super-Alfvénic, sub- and supersonic). With this information, we can estimate the radius of the exoplanet magnetopause and thus the exoplanet unprotected surface. Results. We have conducted a study of the auroral aperture angles for Earth-like exoplanets orbiting the habitable zone of its star, and found different behaviors depending on whether the star is in rotational saturated or unsaturated regimes, with angles of aperture of the auroral ring above or below 36°, respectively, and with different slopes for the linear relation between the auroral aperture angle at the inner edge of the habitable zone versus the difference between auroral aperture angles at the two boundaries of the habitable zone. When the planet is tidally locked, the unprotected angle increases dramatically to values higher than 40° with a low likelihood of keeping its atmosphere. When the impact of stellar wind is produced in the sub-Alfvénic regime, the likelihood of keeping the atmosphere is almost zero for exoplanets orbiting very close to their star, regardless of whether they are saturated or not.

scholarly journals The effects of stellar winds and magnetic fields on exoplanets

2013 ◽  
Vol 9 (S302) ◽  
pp. 228-236 ◽  
Author(s):  
A. A. Vidotto
Keyword(s):  
Solar System ◽  
Interplanetary Medium ◽  
Great Majority ◽  
Stellar Winds ◽  
Stellar Rotation ◽  
Low Mass Stars ◽  
Exoplanetary Systems ◽  
Cool Stars ◽  
Low Mass ◽  
Host Stars

AbstractThe great majority of exoplanets discovered so far are orbiting cool, low-mass stars whose properties are relatively similar to the Sun. However, the stellar magnetism of these stars can be significantly different from the solar one, both in topology and intensity. In addition, due to the present-day technology used in exoplanetary searches, most of the currently known exoplanets are found orbiting at extremely close distances to their host stars (< 0.1 au). The dramatic differences in stellar magnetism and orbital radius can make the interplanetary medium of exoplanetary systems remarkably distinct from that of the Solar System. To constrain interactions between exoplanets and their host-star's magnetised winds and to characterise the interplanetary medium that surrounds exoplanets, more realistic stellar wind models, which account for factors such as stellar rotation and the complex stellar magnetic field configurations of cool stars, must be employed. Here, I briefly review the latest progress made in data-driven modelling of magnetised stellar winds. I also show that the interaction of the stellar winds with exoplanets can lead to several observable signatures, some of which that are absent in our own Solar System.

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.

Sign in / Sign up

Export Citation Format

Share Document