Search for: All records

M dwarfs are ubiquitous in our Galaxy, and the rate at which they host stellar companions, and the properties of these companions, provide a window into the formation and evolution of the star(s), and of any planets that they may host. The Pervasive Overview of “Kompanions” of Every M dwarf in Our Neighborhood (POKEMON) speckle survey of nearby M dwarfs is volume limited from M0V through M9V out to 15 pc, with additional targets at larger distances. In total, 1125 stars were observed, and 455 of these are within the volume-limited, 15 pc sample of M-dwarf primaries. When we combine the speckle observations with known companions from the literature, we find that the stellar multiplicity rate of M dwarfs within 15 pc is 23.5% ± 2.0%, and that the companion rate is 28.8% ± 2.1%. We also find that the projected separation distribution for multiples that are known to host planets peaks at 198 au, while the distribution for multiples that are not yet known to host planets peaks at 5.57 au. This result suggests that the presence of close-in stellar companions inhibits the formation of M-dwarf planetary systems, similar to what has been found for FGK stars.

 

Stellar multiplicity is correlated with many stellar properties, yet multiplicity measurements have proven difficult for the M dwarfs—the most common type of star in our galaxy—due to their faintness and the fact that a reasonably complete inventory of later M dwarfs did not exist until recently. We have therefore carried out the Pervasive Overview of “Kompanions” of Every M dwarf in Our Neighborhood (POKEMON) survey, which made use of the Differential Speckle Survey Instrument on the 4.3 m Lowell Discovery Telescope, along with the NN-EXPLORE Exoplanet Stellar Speckle Imager on the 3.5 m WIYN telescope. The POKEMON sample is volume limited from M0V through M9V out to 15 pc, with additional brighter targets at larger distances. In total, 1125 targets were observed. New discoveries were presented in the first paper in the series. In this second paper in the series, we present all detected companions, gauge our astrometric and photometric precision, and compare our filtered and filterless speckle observations. We find that the majority (58.9%) of the companions we detect in our speckle images are not resolved in Gaia, demonstrating the need for high-resolution imaging in addition to long-term astrometric monitoring. Additionally, we find that the majority (73.2%) of simulated stellar companions would be detectable by our speckle observations. Specifically within 100 au, we find that 70.3% of simulated companions are recovered. Finally, we discuss future directions of the POKEMON survey.

 

We confirm the planetary nature of TOI-5344 b as a transiting giant exoplanet around an M0-dwarf star. TOI-5344 b was discovered with the Transiting Exoplanet Survey Satellite photometry and confirmed with ground-based photometry (the Red Buttes Observatory 0.6 m telescope), radial velocity (the Habitable-zone Planet Finder), and speckle imaging (the NN-Explore Exoplanet Stellar Speckle Imager). TOI-5344 b is a Saturn-like giant planet (ρ= 0.80${}_{-0.15}^{+0.17}$g cm⁻³) with a planetary radius of 9.7 ± 0.5R_⊕(0.87 ± 0.04R_Jup) and a planetary mass of${135}_{-18}^{+17}{M}_{\oplus }$(0.42${}_{-0.06}^{+0.05}{M}_{\mathrm{Jup}}$). It has an orbital period of${3.792622}_{-0.000010}^{+0.000010}$days and an orbital eccentricity of${0.06}_{-0.04}^{+0.07}$. We measure a high metallicity for TOI-5344 of [Fe/H] = 0.48 ± 0.12, where the high metallicity is consistent with expectations from formation through core accretion. We compare the metallicity of the M-dwarf hosts of giant exoplanets to that of M-dwarf hosts of nongiants (≲8R_⊕). While the two populations appear to show different metallicity distributions, quantitative tests are prohibited by various sample caveats.

 

Abstract We confirm the planetary nature of two gas giants discovered by TESS to transit M dwarfs with stellar companions at wide separations. TOI-3984 A ( J = 11.93) is an M4 dwarf hosting a short-period (4.353326 ± 0.000005 days) gas giant ( M p = 0.14 ± 0.03 M J and R p = 0.71 ± 0.02 R J ) with a wide-separation white dwarf companion. TOI-5293 A ( J = 12.47) is an M3 dwarf hosting a short-period (2.930289 ± 0.000004 days) gas giant ( M p = 0.54 ± 0.07 M J and R p = 1.06 ± 0.04 R J ) with a wide-separation M dwarf companion. We characterize both systems using a combination of ground- and space-based photometry, speckle imaging, and high-precision radial velocities from the Habitable-zone Planet Finder and NEID spectrographs. TOI-3984 A b ( T eq = 563 ± 15 K and TSM = 138 − 27 + 29 ) and TOI-5293 A b ( T eq = 675 − 30 + 42 K and TSM = 92 ± 14) are two of the coolest gas giants among the population of hot Jupiter–sized gas planets orbiting M dwarfs and are favorable targets for atmospheric characterization of temperate gas giants and 3D obliquity measurements to probe system architecture and migration scenarios. 

The Transiting Exoplanet Survey Satellite (TESS) mission detected a companion orbiting TIC 71268730, categorized it as a planet candidate, and designated the system TOI-5375. Our follow-up analysis using radial-velocity data from the Habitable-zone Planet Finder, photometric data from Red Buttes Observatory, and speckle imaging with NN-EXPLORE Exoplanet Stellar Speckle Imager determined that the companion is a very low mass star near the hydrogen-burning mass limit with a mass of 0.080 ± 0.002M_☉(83.81 ± 2.10M_J), a radius of${0.1114}_{-0.0050}^{+0.0048}{R}_{☉}$(1.0841${}_{0.0487}^{0.0467}{R}_J$), and brightness temperature of 2600 ± 70 K. This object orbits with a period of 1.721553 ± 0.000001 days around an early M dwarf star (0.62 ± 0.016M_☉). TESS photometry shows regular variations in the host star’s TESS light curve, which we interpreted as an activity-induced variation of ∼2%, and used this variability to measure the host star’s stellar rotation period of${1.9716}_{-0.0083}^{+0.0080}$days. The TOI-5375 system provides tight constraints on stellar models of low-mass stars at the hydrogen-burning limit and adds to the population in this important region.

 

TESS has proven to be a powerful resource for finding planets, including those that orbit the most prevalent stars in our galaxy: M dwarfs. Identification of stellar companions (both bound and unbound) has become a standard component of the transiting planet confirmation process in order to assess the level of light-curve dilution and the possibility of the target being a false positive. Studies of stellar companions have also enabled investigations into stellar multiplicity in planet-hosting systems, which has wide-ranging implications for both exoplanet detection and characterization, as well as for the formation and evolution of planetary systems. Speckle and AO imaging are some of the most efficient and effective tools for revealing close-in stellar companions; we therefore present observations of 58 M-dwarf TOIs obtained using a suite of speckle imagers at the 3.5 m WIYN telescope, the 4.3 m Lowell Discovery Telescope, and the 8.1 m Gemini North and South telescopes. These observations, as well as near-infrared adaptive optics images obtained for a subset (14) of these TOIs, revealed only two close-in stellar companions. Upon surveying the literature, and cross-matching our sample with Gaia, SUPERWIDE, and the catalog from El-Badry et al., we reveal an additional 15 widely separated common proper motion companions. We also evaluate the potential for undetected close-in companions. Taking into consideration the sensitivity of the observations, our findings suggest that the orbital period distribution of stellar companions to planet-hosting M dwarfs is shifted to longer periods compared to the expected distribution for field M dwarfs.

 

We perform an in-depth analysis of the recently validated TOI-3884 system, an M4-dwarf star with a transiting super-Neptune. Using high-precision light curves obtained with the 3.5 m Apache Point Observatory and radial velocity observations with the Habitable-zone Planet Finder, we derive a planetary mass of${32.6}_{-7.4}^{+7.3}{M}_{\oplus }$and radius of 6.4 ± 0.2R_⊕. We detect a distinct starspot crossing event occurring just after ingress and spanning half the transit for every transit. We determine this spot feature to be wavelength dependent with the amplitude and duration evolving slightly over time. Best-fit starspot models show that TOI-3884b possesses a misaligned (λ= 75° ± 10°) orbit that crosses a giant pole spot. This system presents a rare opportunity for studies into the nature of both a misaligned super-Neptune and spot evolution on an active mid-M dwarf.

 

Abstract We confirm the planetary nature of two gas giants discovered by the Transiting Exoplanet Survey Satellite to transit M dwarfs. TOI-3714 ( V = 15.24, J = 11.74) is an M2 dwarf hosting a hot Jupiter ( M p = 0.70 ± 0.03 M J and R p = 1.01 ± 0.03 R J ) on an orbital period of 2.154849 ± 0.000001 days with a resolved white dwarf companion. TOI-3629 ( V = 14.63, J = 11.42) is an M1 dwarf hosting a hot Jupiter ( M p = 0.26 ± 0.02 M J and R p =0.74 ± 0.02 R J ) on an orbital period of 3.936551 − 0.000006 + 0.000005 days. We characterize each transiting companion using a combination of ground-based and space-based photometry, speckle imaging, and high-precision velocimetry from the Habitable-zone Planet Finder and the NEID spectrographs. With the discovery of these two systems, there are now nine M dwarfs known to host transiting hot Jupiters. Among this population, TOI-3714 b ( T eq = 750 ± 20 K and TSM = 98 ± 7) and TOI-3629 b ( T eq = 690 ± 20 K and TSM = 80 ± 9) are warm gas giants amenable to additional characterization with transmission spectroscopy to probe atmospheric chemistry and, for TOI-3714, obliquity measurements to probe formation scenarios.