M Dwarfs Research Articles

Searching Transits Around Red Dwarfs

In this research, researchers aim to find the existence of possible new exoplanets within the various red dwarf systems with masses of 0.1 M/Me 0.3 within 15 parsecs of the Earth. In the sample size of 600, the Team Hypothesized the existence of at least 3-5 previously undiscovered exoplanets due to the red dwarf's properties mentioned above combined with technological advancement, allowing for a more effective analysis method of the existing data. The Researchers intended to use python to access Jupyter labs through which the codes analyze to measure the relative flux graph and with the aid of other programs such as NumPy, lightkurve, BLS, and Doppler shift method. The researchers classified all flux patterns into four different types: Ordinary(theres no worth-noticing feature) flux pattern; Wave pattern, for which the flux distribution in the graph is an approximate adjustment to the sinusoidal mathematical trend with few minimal variations; Transit patterns, graphs which got flux pattern at some specific period ,when researchers find this pattern, they will zoom in the special flux area and employ BLS method to determine whether there exists at least one exo-planet.; Flare patterns, which have a feature of windfall, they have steep and rapid changes in flux as well as patterns. Researchers recorded the fourth type in paper to offer reference materials for later researchers who may be interested in flares. Through analyzing, we found 1 case of unresearched flare and 2 cases of worth-noting patterns, but no new exoplanets were found.

Oxygenic photosynthetic responses of cyanobacteria exposed under an M-dwarf starlight simulator: Implications for exoplanet's habitability.

The search for life on distant exoplanets is expected to rely on atmospheric biosignatures detection, such as oxygen of biological origin. However, it is not demonstrated how much oxygenic photosynthesis, which on Earth depends on visible light, could work under spectral conditions simulating exoplanets orbiting the Habitable Zone of M-dwarf stars, which have low light emission in the visible and high light emission in the far-red/near-infrared. By utilizing cyanobacteria, the first organisms to evolve oxygenic photosynthesis on our planet, and a starlight simulator capable of accurately reproducing the emission spectrum of an M-dwarf in the range 350-900 nm, we could answer this question. We performed experiments with the cyanobacterium Chlorogloeopsis fritschii PCC6912, capable of Far-Red Light Photoacclimation (FaRLiP), which allows the strain to harvest far-red in addition to visible light for photosynthesis, and Synechocystis sp. PCC6803, a species unable to perform this photoacclimation, comparing their responses when exposed to three simulated light spectra: M-dwarf, solar and far-red. We analysed growth and photosynthetic acclimation features in terms of pigment composition and photosystems organization. Finally, we determined the oxygen production of the strains directly exposed to the different spectra. Both cyanobacteria were shown to grow and photosynthesize similarly under M-dwarf and solar light conditions: Synechocystis sp. by utilizing the few photons in the visible, C. fritschii by harvesting both visible and far-red light, activating the FaRLiP response. Our results experimentally show that an M-dwarf light spectrum could support a biological oxygen production similar to that in solar light at the tested light intensities, suggesting the possibility to discover such atmospheric biosignatures on those exoplanets if other boundary conditions are met.

A sub-Neptune planet around TOI-1695 discovered and characterized with SPIRou and TESS

TOI-1695 is a V-mag = 13 M-dwarf star from the northern hemisphere at 45 pc from the Sun, around which a 3.134-day periodic transit signal from a super-Earth candidate was identified in TESS photometry. With a transit depth of 1.3 mmag, the radius of candidate TOI-1695.01 was estimated by the TESS pipeline to be 1.82 R⊕ with an equilibrium temperature of ~620 K. We successfully detected a reflex motion of the star and establish that it is due to a planetary companion at an orbital period consistent with the photometric transit period, thanks to a year-long radial-velocity monitoring of TOI-1695 by the SPIRou infrared spectropolarimeter. We used and compared different methods to reduce and analyze those data. We report a 5.5σ detection of the planetary signal, giving a mass of 5.5±1.0 M⊕ and a radius of 2.03±0.18 R⊕. We derive a mean equilibrium planet temperature of 590±90 K. The mean density of this small planet of 3.6±1.1 g cm−3 is similar (1.7σ lower) than that of the Earth. It leads to a nonnegligible fraction of volatiles in its atmosphere with fH,He = 0.28−0.23+0.46% or fwater = 23±12%. TOI-1695 b is a new sub-Neptune planet at the border of the M-dwarf radius valley that can help test formation scenarios for super-Earth and sub-Neptune-like planets.

Hubble WFC3 Spectroscopy of the Terrestrial Planets L 98–59 c and d: No Evidence for a Clear Hydrogen Dominated Primary Atmosphere

The nearby bright M-dwarf star L 98–59 has three terrestrial-sized planets. One challenge remaining in characterizing atmospheres around such planets is that it is not known a priori whether they possess any atmospheres. Here we report on study of the atmospheres of L 98–59 c and L 98–59 d using near-infrared spectral data from the G141 grism of Hubble Space Telescope (HST)/Wide Field Camera 3. We can reject the hypothesis of a clear atmosphere dominated by hydrogen and helium at a confidence level of ∼3σ for both planets. Thus they could have a primary hydrogen-dominated atmosphere with an opaque cloud layer, or could have lost their primary hydrogen-dominated atmosphere and re-established a secondary thin atmosphere, or have no atmosphere at all. We cannot distinguish between these scenarios for the two planets using the current HST data. Future observations with the James Webb Space Telescope would be capable of confirming the existence of atmospheres around L 98–59 c and d and determining their compositions.

Stellar initial mass function varies with metallicity and time.

Most structural and evolutionary properties of galaxies strongly rely on the stellar initial mass function (IMF), namely the distribution of the stellar mass formed in each episode of star formation1-4. The IMF shapes the stellar population in all stellar systems, and so has become one of the most fundamental concepts of modern astronomy. Both constant and variable IMFs across different environments have been claimed despite a large number of theoretical5-7 and observational efforts8-15. However, the measurement of the IMF in Galactic stellar populations has been limited by the relatively small number of photometrically observed stars, leading to high uncertainties12-16. Here we report a star-counting result based on approximately 93,000 spectroscopically observed M-dwarf stars, an order of magnitude more than previous studies, in the 100-300 parsec solar neighbourhood. We find unambiguous evidence of a variable IMF that depends on both metallicity and stellar age. Specifically, the stellar population formed at early times contains fewer low-mass stars compared with the canonical IMF, independent of stellar metallicities. In more recent times, however, the proportion of low-mass stars increases with stellar metallicity. The variable abundance of low-mass stars in our Milky Way establishes a powerful benchmark for models of star formation and can heavily affect results in Galactic chemical-enrichment modelling, mass estimation of galaxies and planet-formation efficiency.

Photosynthetic Fluorescence from Earthlike Planets around Sunlike and Cool Stars

Remote sensing of the Earth has demonstrated that photosynthesis is traceable as the vegetation red edge (VRE), which is a steep rise in the reflection spectrum of vegetation, and as solar-induced fluorescence. This study examines the detectability of biological fluorescence from two types of photosynthetic pigments, chlorophylls (Chls) and bacteriochlorophylls (BChls), on Earthlike planets with oxygen-rich/poor and anoxic atmospheres around the Sun and M dwarfs. Atmospheric absorption, such as H2O, CH4, O2, and O3, and the VRE obscure the fluorescence emissions from Chls and BChls. We find that the BChl-based fluorescence for wavelengths of 1000–1100 nm, assuming the spectrum of BChl b–bearing purple bacteria, could provide a suitable biosignature, but only in the absence of water cloud coverage or other strong absorbers near 1000 nm. The Chl fluorescence is weaker for several reasons, e.g., spectral blending with the VRE. The apparent reflectance excess is greatly increased in both the Chl and BChl cases around TRAPPIST-1, due to the fluorescence and stellar absorption lines. This could be a promising feature for detecting the fluorescence around ultracool red dwarfs using follow-up ground-based observations at high spectral resolution; however, this would require a long time around Sunlike stars, even for a LUVOIR-like space mission. Moreover, the simultaneous detection of fluorescence and the VRE is the key to identifying traces of photosynthesis, because absorption, reflectance, and fluorescence are physically connected. For further validation of the fluorescence detection, the nonlinear response of biological fluorescence as a function of light intensity could be considered.

Effect of calcium hypochlorite on surface sterilization and seedling growth of Vietnamese coconut varieties

Coconut (Cocos nucifera L.) or 'the tree of life' is one of the most important palm crops due to its versatility. Reduction in coconut productivity due to natural calamity and disease threats has raised the urgent need to develop in vitro techniques that can overcome the obstacles of the traditional breeding method. Embryo culture is one of the earliest in vitro culture techniques applied to practical problems and so far has proved itself to be of great value to breeders. However, contamination is one of the most serious problems that reduces the efficiency in in vitro culture techniques. Thus, appropriate surface sterilization treatments are highly important to in vitro culture establishment. The present study was performed to evaluate the sterilization effect of calcium hypochlorite by comparing with sodium hypochlorite. This study also examined the effects of calcium hypochlorite concentrations on plantlets morphogenesis. The findings revealed that amongst the tested treatments, 0.5% (w/v) calcium hypochlorite was the most effective treatment with the lowest rate of contamination. This treatment also significantly improved shoot and root elongation in comparison with calcium hypochlorite at higher concentrations (3% and 6%, w/v). Thus, this concentration was found to be optimal for surface sterilization of two coconut cultivars - Aromatic and Xiem Red Dwarf. Besides that, the results obtained from this study indicated that 70% (v/v) ethanol was not critical in surface sterilization protocol of coconut embryo culture. This research has provided an improved approach for surface sterilization which was previously dependent on sodium hypochlorite and ethanol.

In the Trenches of the Solar–Stellar Connection. VI. Total EclipSS

The Ecliptic poles Stellar Survey (EclipSS; 2018–2019) collected Hubble Space Telescope/Cosmic Origins Spectrograph (COS) 1150–1420 Å spectra of 49 FGK dwarfs at high ecliptic latitudes. These regions are favored by the scanning programs of the Transiting Exoplanet Survey Satellite (TESS; high-precision optical light curves) and Extended Roentgen Survey with an Imaging Telescope Array (eROSITA; repeated X-ray visits over half a decade), which can provide vital ancillary support in the exploration of high-energy “stellar activity.” The present study is a follow-on, focused on new Chandra/High Resolution Camera 0.1–2.4 keV X-ray pointings, COS 1340–1720 Å spectra, and TESS photometry of the 10 most active EclipSS members, but also including archival X-ray and far-ultraviolet (FUV) observations of 13 representative solar neighborhood FGK dwarfs, together with high-energy irradiances of the Sun, for context. The EclipSS dK+dM binary HD 41004 proved exceptional. The unexpectedly short TESS period (1.3 days) appears to be associated with the red dwarf secondary, possibly about to engulf a close-orbiting brown-dwarf companion. The current study describes the emission-line profiles of a high-resolution subset of the full sample, finding the non-Gaussian line shapes (sharper peaks, broader wings) and redshifts of T ∼ 105 K features to be remarkably independent of activity; quantifies X-ray and FUV “variability bias” based on several multiple-epoch campaigns; builds enhanced flux–flux diagrams (e.g., X-rays versus C iv); and constructs an “XUV” proxy flux, representing the total coronal radiative loss, to test models of the convective turnover time, τ c. The associated Rossby number, Ro, is closely aligned to terrestrial and cosmic magnetic dynamo theories, and offers the prospect of a one-parameter description of stellar high-energy activity (relevant, for example, to host-star ionizing fluxes impacting exoplanets).

First Record and Morphology Study of Red Dwarf Honey Bees Apis Florea Fabricius (1787) in Basra Province

In this study, 25 Morphometric characters of dwarf honey bees Apis florea: 15 were for the body characters and 10 for wing venation, in four geographical areas in the province of Basra. a total Samples of 360 workers, Computer program ImageJ was used to measure Morphometric characters. The results of the statistical analysis of the averages showed a clear difference in the Basra area, as the least of them were in the characters of the Head length and width, femur length, width of the end of tibia, and 1st Wax mirror Length, followed by the Al-Siba area in the characters, tibia length, 3rd tergite length, and 3rd sternite length. As for the wing venation, which are forewing width, No. hamuli, A4 angle, B4 angle, G18 angle, and K19 angle. While the cluster analysis showed the hierarchical grouping method of Basra bees with some regional countries, the Basra bees group aligned with the Iranian bee group with a degree of lineage and genetic distance more than the rest of the groups, this study is considered a preliminary registration and diagnosis of Apes florea in Basra province.

Periodic Variations in the Brightness of the Red Dwarf V647 Her

Periodic Variations in the Brightness of the Red Dwarf V647 Her

Kepler K2 Observations of the Faint, Understudied Polar SDSS J092122.84+203857.1

SDSS J092122.84+203857.1 is a polar-type cataclysmic variable system, consisting of a strongly magnetized white dwarf that accretes from its red dwarf companion. It is also one of just five polars known to have been observed by Kepler during its K2 mission. We analyzed the K2 short-cadence light curve of J0921 and identified a weak, but highly coherent, signal at a frequency of 17.099 cycles day−1, corresponding with the system's reported orbital period. We see no overall variation in the accretion rate across the K2 observation, and both our measurement of the period and the binned orbital profile are very consistent with previous ground-based data.

Predicting ‘Earth-like’ planets around red dwarfs

Predicting ‘Earth-like’ planets around red dwarfs

TOI-3884 b: A rare 6-RE planet that transits a low-mass star with a giant and likely polar spot

The Transiting Exoplanet Survey Satellite mission identified a deep and asymmetric transit-like signal with a periodicity of 4.5 days orbiting the M4 dwarf star TOI-3884. The signal has been confirmed by follow-up observations collected by the ExTrA facility and Las Cumbres Observatory Global Telescope, which reveal that the transit is chromatic. The light curves are well modelled by a host star having a large polar spot transited by a 6-RE planet. We validate the planet with seeing-limited photometry, high-resolution imaging, and radial velocities. TOI-3884 b, with a radius of 6.00 ± 0.18 RE, is the first sub-Saturn planet transiting a mid-M dwarf. Owing to the host star’s brightness and small size, it has one of the largest transmission spectroscopy metrics for this planet size and becomes a top target for atmospheric characterisation with the James Webb Space Telescope and ground-based telescopes.

Publisher's Note: “Platform for probing radiation transport properties of hydrogen at conditions found in the deep interiors of red dwarfs” [Phys. Plasmas 29, 083301 (2022)

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Characterizing and Mitigating Telluric Absorption in Precise Radial Velocities. II. A Study of an M2-type Star

Telluric absorption lines impact the measuring of precise radial velocities (RVs) from high-resolution ground-based spectrographs. In this paper, we simulate the dependence of this impact on stellar spectral type and extend the work of the first paper in this series, which studied a G-type star, to a synthetic M-dwarf star. We quantify the bias in precise RV measurements in the visible and near-infrared (NIR) from the presence of tellurics in a simulated set of observations. We find that M-dwarf RVs are more impacted by tellurics compared to G-type stars. Specifically, for an M-dwarf star, tellurics can induce RV errors of up to 16 cm s−1 in the red optical and in excess of 220 cm s−1 in the NIR. For a G dwarf, the comparable RV systematics are 3 cm s−1 in the red optical and 240 cm s−1 in the NIR. We attribute this relative increase for M-dwarf stars to the increased concordance in wavelength between telluric lines and stellar Doppler information content. We compare the results of our simulation to data collected for Barnard’s star from the iSHELL spectrograph at the NASA Infrared Telescope Facility. This study was conducted as a follow-up to the NASA probe mission concept study EarthFinder.

X-Ray Emission from the Exoplanet Hosting LTT 1445 Triple Star System

JWST will be able to observe the atmospheres of rocky planets transiting nearby M dwarfs. The M-dwarf triple star system LTT 1445, at a distance of 6.86 pc, hosts some of the nearest rocky terrestrial planets. These planets most likely orbit the M 3.5V star LTT 1445A. During a 28.6 ks Chandra ACIS-S3 observation we have: (i) spatially resolved and detected all three stars in the LTT 1445 system; (ii) measured the X-ray luminosity of the individual stars, including LTT 1445A, for the first time; (iii) studied the flux variability of the X-ray sources and found strong variability from the A and C components; and (iv) investigated how the coronal luminosities, temperatures, and volume emission measures vary at different activity levels. Combining these X-ray data with upcoming HST ultraviolet observations will allow a differential emission measure estimation of the star’s extreme-ultraviolet spectrum, thereby facilitating modeling of the rocky planets’ atmospheres.

Measurements of visual double stars with PISCO2 at the Nice 76‐cm refractor in 2013–2014

AbstractWe present relative astrometric and photometric measurements of visual double stars made in 2013–2014 with PISCO2 installed at the 76‐cm refractor of the Côte d'Azur Observatory in Nice (France). Our observation list contains orbital couples as well as double stars whose motion is still uncertain. Three different techniques were used for obtaining measurements: Lucky Imaging, Speckle Interferometry, and the Direct Vector Autocorrelation method. From our observations of 4,864 multiple stars, we obtained 4,952 new measurements with angular separations in the range 0″.1–14″ and an average accuracy of 0″.015. The mean error on the position angles is 1°.0. Most of the position angles were determined without the usual 180° ambiguity with the application of the direct vector autocorrelation technique and/or by inspection of the Lucky images or the long integration files. We managed to routinely monitor faint systems (mV ≈ 9–11) with large magnitude differences (up to ΔmV ≈ 5). We have thus been able to measure 49 systems containing red dwarf stars that had been poorly monitored since their discovery, from which we estimated the stellar masses thanks to Gaia measurements. We also measured the magnitude difference of the two components of 318 double stars with an estimated error of 0.2 mag. Except for a few objects that have been discussed, our measurements are in good agreement with the ephemerides computed with published orbital elements, even for the double stars whose separation is smaller than the diffraction limit. Thanks to good seeing images and with the use of high‐contrast numerical filters, we have also been able to obtain 455 measurements with an angular separation smaller than the diffraction limit of our instrumentation, and consistent with those obtained with larger telescopes. Finally, we report 378 measurements of the 296 new double stars that we found in the files obtained during the observations.

SPECULOOS Northern Observatory: Searching for Red Worlds in the Northern Skies

SPECULOOS is a ground-based transit survey consisting of six identical 1 m robotic telescopes. The immediate goal of the project is to detect temperate terrestrial planets transiting nearby ultracool dwarfs (late M-dwarf stars and brown dwarfs), which could be amenable for atmospheric research with the next generation of telescopes. Here, we report the developments of the northern counterpart of the project—SPECULOOS Northern Observatory, and present its performance during the first three years of operations from mid-2019 to mid-2022. Currently, the observatory consists of one telescope, which is named Artemis. The Artemis telescope demonstrates remarkable photometric precision, allowing it to be ready to detect new transiting terrestrial exoplanets around ultracool dwarfs. Over the period of the first three years after the installation, we observed 96 objects from the SPECULOOS target list for 6000 hr with a typical photometric precision of 0.5%, and reaching a precision of 0.2% for relatively bright non-variable targets with a typical exposure time of 25 s. Our weather downtime (clouds, high wind speed, high humidity, precipitation and/or high concentration of dust particles in the air) over the period of three years was 30% of overall night time. Our actual downtime is 40% because of additional time loss associated with technical problems.

Validation and atmospheric exploration of the sub-Neptune TOI-2136b around a nearby M3 dwarf

Context. The NASA space telescope TESS is currently in the extended mission of its all-sky search for new transiting planets. Of the thousands of candidates that TESS is expected to deliver, transiting planets orbiting nearby M dwarfs are particularly interesting targets since they provide a great opportunity to characterize their atmospheres by transmission spectroscopy. Aims. We aim to validate and characterize the new sub-Neptune-sized planet candidate TOI-2136.01 orbiting a nearby M dwarf (d = 33.36 ± 0.02pc, Teff = 3373 ± 108 K) with an orbital period of 7.852 days. Methods. We use TESS data, ground-based multicolor photometry, and radial velocity measurements with the InfraRed Doppler (IRD) instrument on the Subaru Telescope to validate the planetary nature of TOI-2136.01, and estimate the stellar and planetary parameters. We also conduct high-resolution transmission spectroscopy to search for helium in its atmosphere. Results. We confirm that TOI-2136.01 (now named TOI-2136b) is a bona fide planet with a planetary radius of Rp = 2.20 ± 0.07R⊕ and a mass of Mp = 4.7−2.6+3.1 M⊕. We also search for helium 10830 Å absorption lines and place an upper limit on the equivalent width of <7.8 mÅ and on the absorption signal of <1.44% with 95% confidence. Conclusions. TOI-2136b is a sub-Neptune transiting a nearby and bright star (J = 10.8 mag), and is a potentially hycean planet, which is a new class of habitable planets with large oceans under a H2-rich atmosphere, making it an excellent target for atmospheric studies to understand the formation, evolution, and habitability of the small planets.

Lightning-induced chemistry on tidally-locked Earth-like exoplanets

ABSTRACT Determining the habitability and interpreting atmospheric spectra of exoplanets requires understanding their atmospheric physics and chemistry. We use a 3-D coupled climate-chemistry model, the Met Office Unified Model with the UK Chemistry and Aerosols framework, to study the emergence of lightning and its chemical impact on tidally-locked Earth-like exoplanets. We simulate the atmosphere of Proxima Centauri b orbiting in the Habitable Zone of its M-dwarf star, but the results apply to similar M-dwarf orbiting planets. Our chemical network includes the Chapman ozone reactions and hydrogen oxide (HOx = H + OH + HO2) and nitrogen oxide (NOx = NO + NO2) catalytic cycles. We find that photochemistry driven by stellar radiation (177–850 nm) supports a global ozone layer between 20–50 km. We parametrize lightning flashes as a function of cloud-top height and the resulting production of nitric oxide (NO) from the thermal decomposition of N2 and O2. Rapid dayside convection over and around the substellar point results in lightning flash rates of up to 0.16 flashes km−2 yr−1, enriching the dayside atmosphere below altitudes of 20 km in NOx. Changes in dayside ozone are determined mainly by UV irradiance and the HOx catalytic cycle. ∼45 per cent of the planetary dayside surface remains at habitable temperatures (Tsurf > 273.15K), and the ozone layer reduces surface UV radiation levels to 15 per cent. Dayside–nightside thermal gradients result in strong winds that subsequently advect NOx towards the nightside, where the absence of photochemistry allows NOx chemistry to involve reservoir species. Our study also emphasizes the need for accurate UV stellar spectra to understand the atmospheric chemistry of exoplanets.