Nearby Red Dwarf Research Articles

GJ 367b: A dense, ultrashort-period sub-Earth planet transiting a nearby red dwarf star.

Ultrashort-period (USP) exoplanets have orbital periods shorter than 1 day. Precise masses and radii of USP exoplanets could provide constraints on their unknown formation and evolution processes. We report the detection and characterization of the USP planet GJ 367b using high-precision photometry and radial velocity observations. GJ 367b orbits a bright (V-band magnitude of 10.2), nearby, and red (M-type) dwarf star every 7.7 hours. GJ 367b has a radius of 0.718 ± 0.054 Earth-radii and a mass of 0.546 ± 0.078 Earth-masses, making it a sub-Earth planet. The corresponding bulk density is 8.106 ± 2.165 grams per cubic centimeter—close to that of iron. An interior structure model predicts that the planet has an iron core radius fraction of 86 ± 5%, similar to that of Mercury’s interior.

Multiple Moist Climate Equilibrium States on Arid Rocky M-dwarf Planets: A Last-saturation Tracer Analysis

Abstract Terrestrial-type exoplanets orbiting nearby red dwarf stars (M dwarfs) are the first potentially habitable exoplanets suitable for atmospheric characterization in the near future. Understanding the stability of water in cold-trap regions on such planets is critical because it directly impacts transmission spectroscopy observations, the global energy budget, and long-term surface water evolution. Here we diagnose the humidity distribution in idealized general circulation model simulations of terrestrial-type exoplanets. We use the “tracer of last saturation” technique to study the saturation statistics of air parcels. We find that on synchronously rotating planets the water vapor abundance in the nightside upper troposphere depends weakly on planetary rotation, while more water vapor builds up in the nightside lower troposphere on fast-rotating planets. We then discuss how last-saturation statistics can elucidate the multiple moist climate equilibrium states on synchronously and asynchronously rotating arid planets. We show that the multiple moist climate states arise from the cold-trapping competition between the substellar upper atmosphere and cold surface regions. We find that fast synchronously rotating planets tend to trap surface water on the nightside as a result of their weak atmospheric and strong surface cold traps compared to the slow-rotating case. These results elucidate the nature of the water cycle on arid rocky exoplanets and will aid interpretation of atmospheric observations in the future.

A multiplanet system of super-Earths orbiting the brightest red dwarf star GJ 887.

The closet exoplanets to the Sun provide opportunities for detailed characterization of planets outside the Solar System. We report the discovery, using radial velocity measurements, of a compact multiplanet system of super-Earth exoplanets orbiting the nearby red dwarf star GJ 887. The two planets have orbital periods of 9.3 and 21.8 days. Assuming an Earth-like albedo, the equilibrium temperature of the 21.8-day planet is ~350 kelvin. The planets are interior to, but close to the inner edge of, the liquid-water habitable zone. We also detect an unconfirmed signal with a period of ~50 days, which could correspond to a third super-Earth in a more temperate orbit. Our observations show that GJ 887 has photometric variability below 500 parts per million, which is unusually quiet for a red dwarf.

A nearby multiplanet system

Exoplanets Exoplanets can interact gravitationally with other objects orbiting the same star, affecting their evolution and stability. Studying these effects requires locating systems with multiple planets. Monitoring the nearby red dwarf star GJ 887, Jeffers et al. detected periodic radial velocity signals, indicating the presence of two planets on orbits with periods of about 9 and 22 days and a further candidate planet (see the Perspective by Davies). The inclinations of the orbits are unknown, so only minimum masses could be determined, but those were consistent with both planets being super-Earths—more massive than Earth but less than Neptune. This system is only 3.3 parsecs from the Sun, which should facilitate follow-up with other techniques. Science , this issue p. [1477][1]; see also p. [1432][2] [1]: /lookup/doi/10.1126/science.aaz0795 [2]: /lookup/doi/10.1126/science.abb0217

Stabilization of Dayside Surface Liquid Water via Tropopause Cold Trapping on Arid Slowly Rotating Tidally Locked Planets

Abstract Terrestrial-type exoplanets orbiting nearby red dwarf stars (M dwarfs) are among the best targets for atmospheric characterization and biosignature searches in the near future. Recent evolutionary studies have suggested that terrestrial planets in the habitable zone of M dwarfs are probably tidally locked and have limited surface water inventories as a result of their host stars’ high early luminosities. Several previous climate simulations of such planets have indicated that their remaining water would be transported to the planet’s permanent nightside and become trapped as surface ice, leaving the dayside devoid of water. Here we use a three-dimensional general circulation model with a water cycle and accurate radiative transfer scheme to investigate the surface water evolution on slowly rotating tidally locked terrestrial planets with limited surface water inventories. We show that there is a competition for water trapping between the nightside surface and the substellar tropopause in this type of climate system. Although under some conditions the surface water remains trapped on the nightside as an ice sheet, in other cases liquid water stabilizes in a circular area in the substellar region as a wetland. Planets with 1 bar N2 and atmospheric CO2 levels greater than 0.1 bar retain stable dayside liquid water, even with very small surface water inventories. Our results reveal the diversity of possible climate states on terrestrial-type exoplanets and highlight the importance of surface liquid water detection techniques for future characterization efforts.

Radial velocity follow-up of GJ1132 with HARPS

The source GJ1132 is a nearby red dwarf known to host a transiting Earth-size planet. After its initial detection, we pursued an intense follow-up with the HARPS velocimeter. We now confirm the detection of GJ1132b with radial velocities alone. We refined its orbital parameters, and in particular, its mass (mb = 1.66 ± 0.23 M⊕), density (ρb = 6.3 ± 1.3 g cm−3), and eccentricity (eb < 0.22; 95%). We also detected at least one more planet in the system. GJ1132c is a super-Earth with period Pc = 8.93 ± 0.01 days and minimum mass mc sinic = 2.64 ± 0.44 M⊕. Receiving about 1.9 times more flux than Earth in our solar system, its equilibrium temperature is that of a temperate planet (Teq = 230−300 K for albedos A = 0.75 − 0.00), which places GJ1132c near the inner edge of the so-called habitable zone. Despite an a priori favorable orientation for the system, Spitzer observations reject most transit configurations, leaving a posterior probability <1% that GJ1132c transits. GJ1132(d) is a third signal with period Pd = 177 ± 5 days attributed to either a planet candidate with minimum mass md sin id = 8.4−2.5+1.7 M⊕ or stellar activity. Its Doppler signal is the most powerful in our HARPS time series but appears on a timescale where either the stellar rotation or a magnetic cycle are viable alternatives to the planet hypothesis. On the one hand, the period is different than that measured for the stellar rotation (~125 days), and a Bayesian statistical analysis we performed with a Markov chain Monte Carlo and Gaussian processes demonstrates that the signal is better described by a Keplerian function than by correlated noise. On the other hand, periodograms of spectral indices sensitive to stellar activity show power excess at similar periods to that of this third signal, and radial velocity shifts induced by stellar activity can also match a Keplerian function. We, therefore, prefer to leave the status of GJ1132(d) undecided.

The Solar Neighborhood. XLIII. Discovery of New Nearby Stars with μ < 0.″18 yr−1 (TINYMO Sample)

Abstract We have conducted a novel search of most of the southern sky for nearby red dwarfs having low proper motions, with specific emphasis on those with μ < 0.″18 yr−1, the lower cutoff of Luyten’s classic proper-motion catalog. We used a tightly constrained search of the SuperCOSMOS database and a suite of photometric distance relations for photographic BRI and 2MASS JHK s magnitudes to estimate distances to more than 14 million red dwarf candidates. Here we discuss 29 stars in 26 systems estimated to be within 25 pc, all of which have μ < 0.″18 yr−1, that we have investigated using milliarcsecond astrometry, VRI photometry, and low-resolution spectroscopy. In total, we present the first parallaxes of 20 star systems, 9 of which are within 25 pc. We have additionally identified 14 young M dwarfs, of which 3 are new members of the nearby young moving groups, and 72 new giants, including two new carbon stars. We also present the entire catalog of 1215 sources we have identified by this means.

New Perspectives of our Nearby Red Dwarf Neighbor Wolf 359 from the Kepler K2 Mission

New Perspectives of our Nearby Red Dwarf Neighbor Wolf 359 from the Kepler K2 Mission

The red dwarf pair GJ65 AB: inflated, spinning twins of Proxima

The nearby red dwarf binary GJ65AB (UB+BL Ceti, M5.5Ve+M6Ve) is a cornerstone system to probe the physics of very low mass stars. We present new interferometric measurements of the angular diameters of the two components of GJ65AB with the PIONIER instrument in the H band: thetaUD (A) = 0.558 +/- 0.008 +/- 0.020 mas and thetaUD (B) = 0.539 +/- 0.009 +/- 0.020 mas. They translate into limb-darkened angular diameters of LD (A) = 0.573 +/- 0.021 mas and LD (B) = 0.554 +/- 0.022 mas. From the known parallax, the radii are R(A) = 0.165 +/- 0.006 Rsun and R(B) = 0.159 +/- 0.006 Rsun (sigma(R)/R = 4%). We also observed GJ65AB with the VLT/NACO adaptive optics and refine the orbital parameters and infrared magnitudes of the system. We derive masses for the two components of m(A) = 0.1225 +/- 0.0043 Msun and m(B) = 0.1195 +/- 0.0043 Msun (sigma(m)/m = 4%). To derive the radial and rotational velocities of the two stars, as well as their relative metallicity with respect to Proxima, we also present new individual UVES high resolution spectra. Placing GJ65 A&B in the mass-radius diagram shows that their radii are larger respectively by 14 +/- 4% and 12 +/- 4% compared to expectations from the models by Baraffe et al. (2015). Following Chabrier et al. (2007), we propose that this discrepancy is caused by the inhibition of convective energy transport by a strong internal magnetic field generated by dynamo effect in these two fast rotating stars. A comparison with the almost identical twin but slowly-rotating Proxima strengthens this hypothesis, as the radius of Proxima does not appear inflated compared to models.

Nearby red dwarf stars reveal unexpected protoplanetary disks

Nearby red dwarf stars reveal unexpected protoplanetary disks

THE SOLAR NEIGHBORHOOD. XXXVI. THE LONG-TERM PHOTOMETRIC VARIABILITY OF NEARBY RED DWARFS IN THEVRIOPTICAL BANDS

We present an analysis of long-term photometric variability for nearby red dwarf stars at optical wavelengths. The sample consists of 264 M dwarfs south of decl. = +30 with = 3.96?9.16 and MV 10?20, corresponding to spectral types M2V?M8V, most of which are within 25 pc. The stars have been observed in the VRI filters for ?4?14 yr at the CTIO/SMARTS 0.9 m telescope. Of the 238 red dwarfs within 25 pc, we find that only ?8% are photometrically variable by at least 20 mmag (?2%) in the VRI bands. Only four stars have been found to vary by more than 50 mmag, including GJ 1207 at 8.6 pc, which experienced a single extraordinary flare, and GJ 2006 A, TWA 8 A, and TWA 8 B, which are all young stars beyond 25 pc linked to moving groups. We find that high variability at optical wavelengths over the long term can in fact be used to identify young stars. Overall, however, the fluxes of most red dwarfs at optical wavelengths are steady to a few percent over the long term. The low overall rate of photometric variability for red dwarfs is consistent with results found in previous work on similar stars on shorter timescales, with the body of work indicating that most red dwarfs are only mildly variable. As expected, we find that the degree of photometric variability is greater in the V band than in the R or I bands, but we do not find any obvious trends in variability over the long term with red dwarf luminosity or temperature. We highlight 17 stars that show long-term changes in brightness, sometimes because of flaring activity or spots, and sometimes because of stellar cycles similar to our Sun?s solar cycle. Remarkably, two targets show brightnesses that monotonically increase (G 169-029) or decrease (WT 460AB) by several percent over a decade. We also provide long-term variability measurements for seven M dwarfs within 25 pc that host exoplanets, none of which vary by more than 20 mmag. Both as a population, and for the specific red dwarfs with exoplanets observed here, photometric variability is therefore often not a concern for planetary environments, at least at the optical wavelengths where they emit much of their light.

High-dispersion spectroscopy of extrasolar planets: from CO in hot Jupiters to O 2 in exo-Earths

Ground-based high-dispersion spectroscopy could reveal molecular oxygen as a biomarker gas in the atmospheres of twin-Earths transiting red dwarf stars within the next 25 years. The required contrasts are only a factor of 3 lower than that already achieved for carbon monoxide in hot Jupiter atmospheres today but will need much larger telescopes because the target stars will be orders of magnitude fainter. If extraterrestrial life is very common and can therefore be found on planets around the most nearby red dwarf stars, it may be detectable via transmission spectroscopy with the next-generation extremely large telescopes. However, it is likely that significantly more collecting area is required for this. This can be achieved through the development of low-cost flux collector technology, which combines a large collecting area with a low but sufficient image quality for high-dispersion spectroscopy of bright stars.

Search for a habitable terrestrial planet transiting the nearby red dwarf GJ 1214

High-precision eclipse spectrophotometry of transiting terrestrial exoplanets represents a promising path for the first atmospheric characterizations of habitable worlds and the search for life outside our solar system. The detection of terrestrial planets transiting nearby late-type M-dwarfs could make this approach applicable within the next decade, with soon-to-come general facilities. In this context, we previously identified GJ 1214 as a high-priority target for a transit search, as the transit probability of a habitable planet orbiting this nearby M4.5 dwarf would be significantly enhanced by the transiting nature of GJ 1214 b, the super-Earth already known to orbit the star. Based on this observation, we have set up an ambitious high-precision photometric monitoring of GJ 1214 with the Spitzer Space Telescope to probe the inner part of its habitable zone in search of a transiting planet as small as Mars. We present here the results of this transit search. Unfortunately, we did not detect any other transiting planets. Assuming that GJ 1214 hosts a habitable planet larger than Mars that has an orbital period smaller than 20.9 days, our global analysis of the whole Spitzer dataset leads to an a posteriori no-transit probability of ~ 98%. Our analysis allows us to significantly improve the characterization of GJ 1214 b, to measure its occultation depth to be 70+-35 ppm at 4.5 microns, and to constrain it to be smaller than 205ppm (3-sigma upper limit) at 3.6 microns. In agreement with the many transmission measurements published so far for GJ 1214 b, these emission measurements are consistent with both a metal-rich and a cloudy hydrogen-rich atmosphere.

New neighbours

We present spectra of 36 nearby star candidates and 3 red giant candidates, identified in the DENIS database. 32 of the dwarf candidates are nearby red dwarfs, with spectral types from M 5.5 to M 8.5. Out of 11 targets with low proper motion ( µ< 0. 1a rcsec yr −1 ) but a Reduced Proper Motion above an inclusive threshold, 9 are red dwarfs. The 4 contaminants are all reddened F-K main sequence stars, and could have been eliminated by checking for small well-known high latitude molecular clouds. These stars might be of interest as probes of interstellar absorption. For the red dwarfs we derive spectral types and spectroscopic distances, using a new calibration of the PC3 spectral index to absolute magnitudes in the I, J, H and K photometric bands. We confirm 2 new members of the 12 pc volume (2 new M 8.5), and one M 7.5 NLTT object closer than 10 pc; and show that one quarter of the stars with photometric distances under 30 pc have too small a proper motion for inclusion in the NLTT catalog.

New High Proper Motion Stars from the Digitized Sky Survey. III. Stars with Proper Motions 0."45 &lt; μ &lt; 2."0 yr-1South of Declination -30°

We report the discovery of 182 southern stars with proper motion larger than 045 yr-1. The stars were found in an expansion of the SUPERBLINK proper-motion survey to 8980 deg2 south of decl. = -30?. The new high proper motion stars include 123 objects with ? > 05 yr-1 and 5 with ? > 10 yr-1. These newfound stars consist of a variety of nearby red dwarfs and white dwarfs and (slightly more distant) red halo subdwarfs, and they are all prime targets for follow-up spectroscopic and astrometric (parallax) observations. Comparison with previous proper-motion surveys in the southern sky suggests that SUPERBLINK has a recovery rate between 80% and 90% at southern declinations for stars with red magnitude 10 mag < RF < 19 mag and proper motion in the range 05 < ? < 20 yr-1. This survey makes a significant addition to the census of high proper motion stars at southern declinations.

The Solar Neighborhood. X. New Nearby Stars in the Southern Sky and Accurate Photometric Distance Estimates for Red Dwarfs

Photometric VRI and spectroscopic (6000-9500 A) observations of high proper motion stars discovered during the first phase of the SuperCOSMOS RECONS (SCR) search are used to estimate accurate distances to eight new nearby red dwarfs, including probable 10 pc sample members SCR 1845-6357 (M8.5V at 4.6 pc), the binary SCR 0630-7643AB (M6.0VJ at 7.0 pc), and SCR 1138-7721 (M5.0V at 9.4 pc). Distance estimates are determined using a suite of new photometric color-Mk relations defined using a robust set of nearby stars with accurate VRIJHK photometry and trigonometric parallaxes. These relations are utilized, with optical and infrared photometry, to estimate distances on a uniform system (generally good to 15%) for two additional samples of red nearby star candidates: several recently discovered members of the solar neighborhood, and known faint stars with proper motions in excess of 1.0/yr south of DEC = -57.5. Of those without accurate trigonometric parallax measurements, there are five stars in the first sample and three in the second that are likely to be within 10 pc. The two nearest are SO 0253+1652 (M7.0V at 3.7 pc) and DEN 1048-3956 (M8.5V at 4.5 pc). When combined with SCR 1845-6357, these three stars together represent the largest increase in the 5 pc sample in several decades. Red spectra are presented for the red dwarfs and types are given on the RECONS standard spectral system. Red spectra are also given for two new nearby white dwarfs for which we estimate distances from the photometry of less than 20 pc -- WD 0141-675 (LHS 145, 9.3 pc) and SCR 2012-5956 (17.4 pc). WD 0141-675 brings the total number of systems nearer than 10 pc discussed in this paper to 12.

Search for nearby stars among proper motion stars selected by optical-to-infrared photometry

We present the discovery of a previously unknown very nearby star - LHS 2090 at a distance of only d=6 pc. In order to find nearby (i.e. d < 25 pc) red dwarfs, we re-identified high proper motion stars ($\mu >$ 0.18 arcsec/yr) from the NLTT catalogue (Luyten \cite{luyten7980}) in optical Digitized Sky Survey data for two different epochs and in the 2MASS data base. Only proper motion stars with large $R-K_s$ colour index and with relatively bright infrared magnitudes ($K_s<10$) were selected for follow-up spectroscopy. The low-resolution spectrum of LHS 2090 and its large proper motion (0.79 arcsec/yr) classify this star as an M6.5 dwarf. The resulting spectroscopic distance estimate from comparing the infrared $JHK_s$ magnitudes of LHS 2090 with absolute magnitudes of M6.5 dwarfs is $6.0\pm1.1$ pc assuming an uncertainty in absolute magnitude of $\pm$0.4 mag.

On the Role of dK and dM Stars in Piling up the Total Mass of Star Clusters

Although many projects were aimed at identifying nearby red dwarfs, the catalogues may be complete up to a limiting distance of 5 pc only and may be reliable to 10 pc. From recent observations it is evident that their absolute visual brightness (MV) ranges from about 6 to at least 18.5 what means that an average dK0 star is at least 100,000 times brighter than red dwarfs of the latest spectral subclasses. The photon detecting efficiency of our instruments is to be increased that these can measure late dM stars from the same distance from which dK stars can be analysed now. Another solution is offered by the flare-active red dwarfs which may be 1000 times brighter during their flare ups than usually.

A Study of the Motion of the Nearby Red Dwarf Lalande 21185

AbstractA series of photographic observations spanning the interval 1962 – 1991 have been examined in a study of Lalande 21185, suspected to be a double or multiple object. The observed value of secular acceleration corresponds to the radial velocity of this star. The perturbations in proper motion with suspected period of 8 years have not been confirmed.

UBVRI photometry of red stars

view Abstract Citations (19) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS UBVRI Photometry of Red Stars Celis S., L. Abstract A total of 50 Mira- and SR-type red variable stars were observed by means of the photoelectric photometry UBVRI Kron-Cousins system. In addition, 15 nearby red dwarf stars having spectral subtypes similar to those of Mira stars at maximum were observed in order to show that the conversion of the natural system into the Landolt (1983) standard system can be made for stars as red as the Mira variables, in spite of the shortage of standard late M-type stars. The relationship function and spectral type-color index scale on the Johnson system was converted into the present system. By means of VRI photometry, the spectral subtype can immediately be determined in different phases of the light curve. SR variables have the same color indices and spectral subclasses as Mira variables. Publication: The Astrophysical Journal Supplement Series Pub Date: March 1986 DOI: 10.1086/191103 Bibcode: 1986ApJS...60..879C Keywords: Late Stars; Red Dwarf Stars; Stellar Spectra; Stellar Spectrophotometry; Ubv Spectra; Variable Stars; Astronomical Catalogs; Data Reduction; Electrophotometry; M Stars; Mira Variables; Spectrum Analysis; Stellar Color; Astronomy; PHOTOMETRY; STARS: LATE-TYPE; STARS: LONG-PERIOD VARIABLES; STARS: SEMIREGULAR VARIABLES full text sources ADS | data products SIMBAD (62) GCPD (1)