scholarly journals Photochemistry of Venus-like Planets Orbiting K- and M-dwarf Stars

2021 ◽  
Vol 922 (1) ◽  
pp. 44
Author(s):  
Sean Jordan ◽  
Paul B. Rimmer ◽  
Oliver Shorttle ◽  
Tereza Constantinou
Keyword(s):  
Effective Temperature ◽  
Spectral Characteristics ◽  
Cloud Layer ◽  
Dwarf Stars ◽  
Stellar Spectra ◽  
Exoplanetary Systems ◽  
Low Mass ◽  
M Dwarf Stars ◽  
M Dwarf ◽  
Host Stars

Abstract Compared to the diversity seen in exoplanets, Venus is a veritable astrophysical twin of the Earth; however, its global cloud layer truncates features in transmission spectroscopy, masking its non-Earth-like nature. Observational indicators that can distinguish an exo-Venus from an exo-Earth must therefore survive above the cloud layer. The above-cloud atmosphere is dominated by photochemistry, which depends on the spectrum of the host star and therefore changes between stellar systems. We explore the systematic changes in photochemistry above the clouds of Venus-like exoplanets orbiting K-dwarf or M-dwarf host stars, using a recently validated model of the full Venus atmosphere (0–115 km) and stellar spectra from the Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems (MUSCLES) Treasury survey. SO2, OCS, and H2S are key gas species in Venus-like planets that are not present in Earth-like planets, and could therefore act as observational discriminants if their atmospheric abundances are high enough to be detected. We find that SO2, OCS, and H2S all survive above the cloud layer when irradiated by the coolest K dwarf and all seven M dwarfs, whereas these species are heavily photochemically depleted above the clouds of Venus. The production of sulfuric acid molecules that form the cloud layer decreases for decreasing stellar effective temperature. Less steady-state photochemical oxygen and ozone forms with decreasing stellar effective temperature, and the effect of chlorine-catalyzed reaction cycles diminish in favor of HO x and SO x catalyzed cycles. We conclude that trace sulfur gases will be prime observational indicators of Venus-like exoplanets around M-dwarf host stars, potentially capable of distinguishing an exo-Venus from an exo-Earth.

scholarly journals Optical Chromospheric Spectral Lines in K and M Dwarf Stars

1989 ◽  
Vol 104 (2) ◽  
pp. 75-78
Author(s):  
R.D. Robinson ◽  
L.E. Cram
Keyword(s):  
Heating Rate ◽  
Spectral Resolution ◽  
Effective Temperature ◽  
Spectral Lines ◽  
High Spectral Resolution ◽  
Dwarf Stars ◽  
M Dwarf Stars ◽  
M Dwarf

AbstractObservations are reported of the Ca II resonance lines and II α in dK and dM stars, made with high S/N ratio and high spectral resolution. Ca II emission is found in all stars observed, and those having weak Ca II exhibit marked Hα absorption. It is found that the strengths of the two kinds of chromospheric, lines are not tightly correlated, an effect which can be shown to be independent of the effective temperature of the stars. The result implies that a one-parameter description (e.g. heating rate) of the chromospheres is not viable. While lateral inhomogeneities are likely to be an important second parameter, we also suggest that the Hα line may be formed in a region considerable higher that in which the Ca II lines are formed.

scholarly journals Simulations of starspot anomalies within TESS exoplanetary transit light curves

2019 ◽  
Vol 630 ◽  
pp. A114 ◽  
Author(s):  
J. Tregloan-Reed ◽  
E. Unda-Sanzana
Keyword(s):  
Light Curve ◽  
Detection Limits ◽  
Mean Amplitude ◽  
Light Curves ◽  
Dwarf Stars ◽  
Spotted Stars ◽  
M Dwarf Stars ◽  
M Dwarf ◽  
The Relationship ◽  
Host Stars

Context. The primary targets of the NASA Transiting Exoplanet Survey Satellite (TESS) are K and M dwarf stars within our solar neighbourhood. Young K and M dwarf stars are known to exhibit a high starspot coverage (≈50%), however, older stars are known to show fewer starspots. This implies that TESS transit light curves at 2 min cadence may contain starspot anomalies, and if so, will require transit-starspot models to determine accurately the properties of the system. Aims. The goals are to determine if starspot anomalies can manifest in TESS transit light curves, to determine the detection limits of the starspot anomalies, and to examine the relationship between the change in flux caused by the starspot anomaly and the planetary transit. Methods. We conducted 20 573 simulations of planetary transits around spotted stars using the transit-starspot model, PRISM. In total 3888 different scenarios were considered using three different host star spectral types, M4V, M1V, and K5V. The mean amplitude of the starspot anomaly was measured and compared to the photometric precision of the light curve to determine if the characteristic “blip” of the starspot anomaly was noticeable in the light curve. Results. The simulations show that starspot anomalies are observable in TESS 2 min cadence data. The smallest starspot detectable in TESS transit light curves has a radius of ≈ 1900 km. The starspot detection limits for the three host stars are 4900 ± 1700 km (M4V), 13 800 ± 6000 km (M1V), and 15 900 ± 6800 km (K5V). The smallest change in flux of the starspot (ΔFspot = 0.00015 ± 0.00001) can be detected when the ratio of planetary to stellar radii k = 0.082 ± 0.004. Conclusions. The results confirm known dependencies between the amplitude of the starspot anomaly and the photometric parameters of the light curve. The results facilitated the characterisation of the relationship between the change in flux of the starspot anomaly and the change in flux of the planetary transit for TESS transit light curves.

scholarly journals Exploring the possibility of Peter Pan discs across stellar mass

2021 ◽  
Author(s):  
Martijn J C Wilhelm ◽  
Simon Portegies Zwart
Keyword(s):  
Mass Loss ◽  
Stellar Mass ◽  
Radiation Environment ◽  
Peter Pan ◽  
Dwarf Stars ◽  
Star Mass ◽  
Stellar Masses ◽  
M Dwarf Stars ◽  
M Dwarf ◽  
Host Stars

Abstract Recently, several accreting M dwarf stars have been discovered with ages far exceeding the typical protoplanetary disc lifetime. These ‘Peter Pan discs’ can be explained as primordial discs that evolve in a low-radiation environment. The persistently low masses of the host stars raise the question whether primordial discs can survive up to these ages around stars of higher mass. In this work we explore the way in which different mass loss processes in protoplanetary discs limit their maximum lifetimes, and how this depends on host star mass. We find that stars with masses ≲ 0.6 M⊙ can retain primordial discs for ∼50 Myr. At stellar masses ≳ 0.8 M⊙, the maximum disc lifetime decreases strongly to below 50 Myr due to relatively more efficient accretion and photoevaporation by the host star. Lifetimes up to 15 Myr are still possible for all host star masses up to ∼2 M⊙. For host star masses between 0.6 and 0.8 M⊙, accretion ceases and an inner gap forms before 50 Myr in our models. Observations suggest that such a configuration is rapidly dispersed. We conclude that Peter Pan discs can only occur around M dwarf stars.

scholarly journals Planet formation around M dwarfs via disc instability

2020 ◽  
Vol 633 ◽  
pp. A116
Author(s):  
Anthony Mercer ◽  
Dimitris Stamatellos
Keyword(s):  
Planet Formation ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
Dwarf Stars ◽  
Low Mass ◽  
Protostellar Discs ◽  
Stellar Masses ◽  
M Dwarf Stars ◽  
Core Accretion ◽  
M Dwarf

Context. Around 30 per cent of the observed exoplanets that orbit M dwarf stars are gas giants that are more massive than Jupiter. These planets are prime candidates for formation by disc instability. Aims. We want to determine the conditions for disc fragmentation around M dwarfs and the properties of the planets that are formed by disc instability. Methods. We performed hydrodynamic simulations of M dwarf protostellar discs in order to determine the minimum disc mass required for gravitational fragmentation to occur. Different stellar masses, disc radii, and metallicities were considered. The mass of each protostellar disc was steadily increased until the disc fragmented and a protoplanet was formed. Results. We find that a disc-to-star mass ratio between ~0.3 and ~0.6 is required for fragmentation to happen. The minimum mass at which a disc fragment increases with the stellar mass and the disc size. Metallicity does not significantly affect the minimum disc fragmentation mass but high metallicity may suppress fragmentation. Protoplanets form quickly (within a few thousand years) at distances around ~50 AU from the host star, and they are initially very hot; their centres have temperatures similar to the ones expected at the accretion shocks around planets formed by core accretion (up to 12 000 K). The final properties of these planets (e.g. mass and orbital radius) are determined through long-term disc-planet or planet–planet interactions. Conclusions. Disc instability is a plausible way to form gas giant planets around M dwarfs provided that discs have at least 30% the mass of their host stars during the initial stages of their formation. Future observations of massive M dwarf discs or planets around very young M dwarfs are required to establish the importance of disc instability for planet formation around low-mass stars.

scholarly journals Activity-Induced Radial Velocity Variation of M Dwarf Stars

2012 ◽  
Vol 8 (S293) ◽  
pp. 197-200
Author(s):  
Jan Marie Andersen ◽  
Heidi Korhonen
Keyword(s):  
Radial Velocity ◽  
Magnetic Activity ◽  
Velocity Variation ◽  
M Dwarfs ◽  
Dwarf Stars ◽  
Highly Active ◽  
Radial Velocity Variation ◽  
Low Mass ◽  
M Dwarf Stars ◽  
M Dwarf

AbstractStellar magnetic activity manifests itself in a variety of ways including starspots–cool, dark regions on the stellar surface. Starspots can cause variations (‘jitter’) in spectral line-profiles which can mimic the radial velocity (RV) variations caused by an orbiting planet, or create RV noise that can drown out a planetary signature. Cool, low-mass M dwarf stars can be highly active, which can make detection of potentially habitable planets around these stars difficult. We investigate radial velocity variations caused by different activity (spot) patterns on M dwarf stars in order to determine the limits of detectability for small planets orbiting active M dwarfs. We report on our progress toward the aim of answering the following questions: What types of spot patterns are realistic for M dwarf stars? What effect will spots have on M dwarf RV measurements? Can jitter from M dwarf spots mimic planetary signals? What is the ideal observing wavelength to reduce M dwarf jitter?

scholarly journals HADES RV programme with HARPS-N at TNG

2020 ◽  
Vol 644 ◽  
pp. A68
Author(s):  
J. Maldonado ◽  
G. Micela ◽  
M. Baratella ◽  
V. D’Orazi ◽  
L. Affer ◽  
...  
Keyword(s):  
High Resolution ◽  
Stellar Mass ◽  
M Dwarfs ◽  
Dwarf Stars ◽  
Large Sample ◽  
Abundance Trends ◽  
Low Mass ◽  
M Dwarf Stars ◽  
First Time ◽  
M Dwarf

Context. Most of our current knowledge on planet formation is still based on the analysis of main sequence, solar-type stars. Conversely, detailed chemical studies of large samples of M dwarfs hosting planets are still missing. Aims. Correlations exist between the presence of different types of planets around FGK stars and metallicity, individual chemical abundance, and stellar mass. We aim to test whether or not these correlations still hold for the less-massive M dwarf stars. Methods to determine stellar abundances of M dwarfs from high-resolution optical spectra in a consistent way are still missing. The present work is a first attempt to fill this gap. Methods. We analyse a large sample of M dwarfs with and without known planetary companions in a coherent and homogeneous way. We develop for the first time a methodology to determine stellar abundances of elements other than iron for M dwarf stars from high-resolution optical spectra. Our methodology is based on the use of a principal component analysis and sparse Bayesian methods. We made use of a set of M dwarfs orbiting around an FGK primary with known abundances to train our methods. We applied our methods to derive stellar metalliticies and abundances of a large sample of M dwarfs observed within the framework of current radial-velocity surveys. We then used a sample of nearby FGK stars to cross-validate our technique by comparing the derived abundance trends in the M dwarf sample with those found on the FGK stars. Results. The metallicity distribution of the different subsamples reveals a correlation between the metallicities of M dwarfs and their probability of hosting giant planets. We also find a correlation between this latter probability and stellar mass. M dwarfs hosting low-mass planets do not seem to follow the so-called planet–metallicity correlation. We also find that the frequency of low-mass planets does not depend on the mass of the stellar host. These results appear to be in agreement with those of previous works. However, we note that for giant-planet hosts our metallicities predict a weaker planet–host metallicity correlation but a stronger mass-dependency than corresponding values derived from photometric results. We show for the first time that there seems to be no differences between M dwarfs with and without known planets in terms of their abundance distributions of elements different from iron. Conclusions. Our data show that low-mass stars with planets follow the same metallicity, mass, and abundance trends as their FGK counterparts, which are usually explained within the framework of core-accretion models.

scholarly journals Effective temperature – radius relationship of M dwarfs

2019 ◽  
Vol 626 ◽  
pp. A32 ◽  
Author(s):  
S. Cassisi ◽  
M. Salaris
Keyword(s):  
Effective Temperature ◽  
Mass Star ◽  
M Dwarfs ◽  
Dwarf Stars ◽  
Fundamental Parameters ◽  
Convective Structures ◽  
Smooth Change ◽  
Theoretical Predictions ◽  
M Dwarf Stars ◽  
M Dwarf

M-dwarf stars provide very favourable conditions for finding habitable worlds beyond our solar system. The estimation of the fundamental parameters of the transiting exoplanets relies on the accuracy of the theoretical predictions for radius and effective temperature of the host M dwarf, therefore it is important to conduct multiple empirical tests of very low-mass star (VLM) models. These stars are the theoretical counterpart of M dwarfs. Recent determinations of mass, radius, and effective temperature of a sample of M dwarfs of known metallicity have disclosed an apparent discontinuity in the effective temperature-radius diagram that corresponds to a stellar mass of about 0.2 M⊙. This discontinuity has been ascribed to the transition from partially convective to fully convective stars. In this paper we compare existing VLM models to these observations, and find that theory does not predict any discontinuity at around 0.2 M⊙, but a smooth change in slope of the effective temperature-radius relationship around this mass value. The appearance of a discontinuity is due to naively fitting the empirical data with linear segments. Moreover, its origin is not related to the transition to fully convective structures. We find that this feature is instead an empirical signature for the transition to a regime where electron degeneracy provides an important contribution to the stellar equation of state, and it constitutes an additional test of the consistency of the theoretical framework for VLM models.

scholarly journals An Astrobiological Experiment to Explore the Habitability of Tidally Locked M-Dwarf Planets

2012 ◽  
Vol 8 (S293) ◽  
pp. 192-196
Author(s):  
Daniel Angerhausen ◽  
Haley Sapers ◽  
Eugenio Simoncini ◽  
Stefanie Lutz ◽  
Marcelo da Rosa Alexandre ◽  
...  
Keyword(s):  
Academic Research ◽  
Environmental Parameters ◽  
Climate Simulation ◽  
Habitable Zone ◽  
Dwarf Stars ◽  
Dwarf Planets ◽  
Late Type Star ◽  
M Dwarf Stars ◽  
M Dwarf ◽  
Simulation Chamber

AbstractWe present a summary of a three-year academic research proposal drafted during the Sao Paulo Advanced School of Astrobiology (SPASA) to prepare for upcoming observations of tidally locked planets orbiting M-dwarf stars. The primary experimental goal of the suggested research is to expose extremophiles from analogue environments to a modified space simulation chamber reproducing the environmental parameters of a tidally locked planet in the habitable zone of a late-type star. Here we focus on a description of the astronomical analysis used to define the parameters for this climate simulation.

Coronal Structure in M Dwarf Stars

1996 ◽  
pp. 81-82
Author(s):  
M. S. Giampapa ◽  
R. Rosner ◽  
V. Kashyap ◽  
T. A. Fleming ◽  
J. H. M. M. Schmitt ◽  
...  
Keyword(s):  
Coronal Structure ◽  
Dwarf Stars ◽  
M Dwarf Stars ◽  
M Dwarf

scholarly journals The habitability of stagnant-lid Earths around dwarf stars

2019 ◽  
Vol 625 ◽  
pp. A12 ◽  
Author(s):  
Mareike Godolt ◽  
Nicola Tosi ◽  
Barbara Stracke ◽  
John Lee Grenfell ◽  
Thomas Ruedas ◽  
...  
Keyword(s):  
Water Loss ◽  
Main Sequence ◽  
Extrasolar Planets ◽  
Water Reservoir ◽  
Habitable Zone ◽  
High Luminosity ◽  
Dwarf Stars ◽  
Surface Conditions ◽  
M Dwarf Stars ◽  
M Dwarf

Context. The habitability of a planet depends on various factors, such as the delivery of water during its formation, the co-evolution of the interior and the atmosphere, and the stellar irradiation which changes in time. Aims. Since an unknown number of rocky extrasolar planets may operate in a one-plate convective regime, i.e. without plate tectonics, our aim is to understand the conditions under which planets in such a stagnant-lid regime may support habitable surface conditions. Understanding the interaction of the planetary interior and outgassing of volatiles in combination with the evolution of the host star is crucial to determining the potential habitability. M-dwarf stars in particular possess a high-luminosity pre-main sequence phase that endangers the habitability of planets around them via water loss. We therefore explore the potential of secondary outgassing from the planetary interior to rebuild a water reservoir allowing for habitability at a later stage. Methods. We compute the boundaries of the habitable zone around M-, K-, G-, and F-dwarf stars using a 1D cloud-free radiative-convective climate model accounting for the outgassing history of CO2 and H2O from an interior evolution and outgassing model for different interior compositions and stellar luminosity evolutions. Results. The outer edge of the habitable zone strongly depends on the amount of CO2 outgassed from the interior, while the inner edge is mainly determined via the stellar irradiation, as soon as a sufficiently large water reservoir has been outgassed. A build-up of a secondary surface and atmospheric water reservoir for planets around M-dwarf stars is possible even after severe water loss during the high-luminosity pre-main sequence phase as long as some water has been retained within the mantle. For small mantle water reservoirs, between 62 and 125 ppm, a time delay in outgassing from the interior permits such a secondary water reservoir build-up especially for early and mid-M dwarfs because their pre-main sequence lifetimes are shorter than the outgassing timescale. Conclusions. We show that Earth-like stagnant-lid planets allow for habitable surface conditions within a continuous habitable zone that is dependent on interior composition. Secondary outgassing from the interior may allow for habitability of planets around M-dwarf stars after severe water loss during the high-luminosity pre-main sequence phase by rebuilding a surface water reservoir.

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