Search

Stellar activity poses one of the main obstacles for the detection and characterisation of exoplanets around cool stars, as it deforms the absorption line profiles of stellar spectra creating signals that can hide or mimic the presence of companions. A wide variety of techniques are being developed with the aim of disentangling signals of stellar and planetary origins. These range from the decorrelation or modelling of the activity signals in the radial velocity (RV) time series, to the RV extraction using carefully selected wavelength regions of the stellar spectrum which are less affected by activity. In this work, we analyse the effects of activity on individual absorption features present on the optical spectra of active M dwarf stars. By studying the correlations between the individual line RVs and activity indicators, we are able to classify the observed lines according to their sensitivity to activity. This allows us to select differently affected lines and use them to compute RVs for which we mitigate or enhance the activity signal to varying degrees. We also observe that the same lines on similar stars show different sensitivities to activity, suggesting the generalisation of a line list a challenging endeavour.

Stellar activity is ubiquitous in M dwarfs. It is a notorious nuisance for high-precision radial velocity planet searches and produces hazardous environments for the atmospheres of planets orbiting these stars. The characterization of the temperature structure of the chromosphere is imperative to understand the upper atmosphere of late-type stars and its impact on their observed spectra. Using the stellar atmosphere code PHOENIX, we constructed a set of 1D chromospheric models with empirical temperature structure to simultaneously fit the lines of Na I D2, H\(\alpha\), and the bluest Ca II infrared triplet line in a sample of 50 M2-3 dwarfs observed by CARMENES (Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Échelle Spectrographs). For the inactive stars, we find good agreement with individual models with a temperature structure corresponding to modified VAL C models. Reproducing the chromospheric lines of the active stars requires linear combinations of an inactive and an active model component, from which we also obtain surface filling factors for the respective components. For stars observed at different activity levels, our modeling yields a significant correlation between the surface filling factor of the active model component and the activity level. Although the models are not optimized for the He I infrared line at 10 830 Å, the best-fit models also give an adequate prediction of the respective line absorption for most stars of the stellar sample. Furthermore, we performed a detailed analysis of the He I infrared line behavior in prescribed model configurations with different levels of activity. The behavior of the He I infrared line strengths as a function of the respective EUV radiation shows the need of the mechanism of photoionization and recombination to form the line for inactive models, while collisions start to contribute for more active models., {"references":["Hintz, D. et al. (2019), A&A, 623, A136","Hintz, D. et al. (2020), A&A, 638, A115","Vernazza, J. E. et al. (1981), ApJS, 45, 635V","Hauschildt, P. H. (1992), JQSRT, 47, 433","Hauschildt, P. H. (1993), JQSRT, 50, 301","Hauschildt, P. H. & Baron, E. (1999), JCoAM, 109, 41","Quirrenbach, A. et al. (2018), SPIE Conf. Ser., 10702, 107020W","Andretta, V. & Jones, H. P. (1997), ApJ, 489, 375"]}

We study the variability of M dwarfs using data collected simultaneously from the Transiting Exoplanet Survey Satellite (TESS) in the optical band and the extended ROentgen Survey with an Imaging Telescope Array (eROSITA) in X-rays. Both TESS and eROSITA perform an all-sky survey, with long exposure observations at the ecliptic poles. We selected M dwarfs from the two-minute target list in the TESS Southern Continuous Viewing Zone (SCVZ) for our sample. Here, we study a sub-sample with the brightest and most variable M dwarfs that have simultaneous TESS and eROSITA light curves and we present our first results on flares seen in both wavebands., {"references":["Stelzer, B. et al. (2016), MNRAS, 463 (2), 1844-1864","Raetz, S. et al. (2020), A&A, 637, A22","Stelzer, B. et al. (2022), A&A, 665, A30","Davenport, James R. A. et al. (2014), ApJ, 797, 122"]}

There are numerous examples in the literature of low-mass stars (, {"references":["Charbonneau D., Deming D., 2007, preprint (arXiv:0706.1047)","Quirrenbach A. et al., 2014, in Ramsay S. K., McLean I. S., Takami H., eds, SPIE Conf. Ser. Vol. 9147, Ground-based and Airborne Instrumentation for Astronomy V. SPIE, Bellingham, p. 91471F","Santos N. C., Barros S. C. C., Demangeon O. D. S., Faria J. P., 2020, Detection and Characterization Methods of Exoplanets. Oxford Univ. Press, Oxford, p. 189","Delrez L. et al., 2018, in Marshall H. K., Spyromilio J., eds, SPIE Conf. Ser. Vol. 10700, Ground-based and Airborne Telescopes VII. SPIE, Bellingham, p.107001I","Gillon M. et al., 2017, Nature, 542, 456","Casagrande L., Flynn C., Bessell M., 2008, MNRAS, 389, 585","Spada F., Demarque P., Kim Y. C., Sills A., 2013, ApJ, 776, 87","Torres G., Andersen J., Gimenez ´ A., 2010, A&AR, 18, 67","Kesseli A. Y., Muirhead P. S., Mann A. W., Mace G., 2018, AJ, 155, 225","Chabrier G., Gallardo J., Baraffe I., 2007, A&A, 472, L17","Fernandes C. S., et al., 2019, ApJ, 879, 94","Ribas I., 2006, Ap&SS, 304, 89","Swayne M. I., et al., 2021, MNRAS, 506, 306","Maxted P. F. L., et al., 2022, MNRAS, 513, 6042","von Boetticher A. et al., 2019, A&A, 625, A150","Baraffe I., Homeier D., Allard F., Chabrier G., 2015, A&A, 577, A42","Sebastian D., et al., 2022 MNRAS, stac2565,"]}

This thesis focus on the interaction between M dwarf stellar winds and Galactic cosmic rays and the possible effects on the habitability of exoplanets. We use numerical simulations to describe the stellar winds of M dwarfs using observable constraints, such as the mass-loss rate, X-ray luminosity, and magnetic field strength/flux. Additionally, we use numerical simulations to describe the propagation of Galactic cosmic rays within M dwarf planetary systems. With these simulations, we can calculate the flux of Galactic cosmic rays reaching exoplanet magnetospheres/atmospheres. Measuring cosmic ray fluxes in exoplanet atmospheres is yet not possible, but cosmic rays are an important ingredient in the context of planetary habitability. For this reason, quantifying these fluxes is essential to complete the habitability “puzzle”. Future exoplanet atmosphere observations with space telescopes, such as the JWST and the ARIEL, will enable us to constrain cosmic ray fluxes in exoplanet atmospheres.

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 (HO$_{\mathrm{x}}$=H+OH+HO$_2$) and nitrogen oxide (NO$_{\mathrm{x}}$=NO+NO$_2$) catalytic cycles. We find that photochemistry driven by stellar radiation (177-850 nm) supports a global ozone layer between 20-50 km. We parameterise lightning flashes as a function of cloud-top height and the resulting production of nitric oxide (NO) from the thermal decomposition of N$_2$ and O$_2$. 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 NO$_{\mathrm{x}}$. Changes in dayside ozone are determined mainly by UV irradiance and the HO$_{\mathrm{x}}$ catalytic cycle. ~45% of the planetary dayside surface remains at habitable temperatures (T$_{\mathrm{surf}}$>273.15 K) and the ozone layer reduces surface UV radiation levels to 15%. Dayside-nightside thermal gradients result in strong winds that subsequently advect NO$_{\mathrm{x}}$ towards the nightside, where the absence of photochemistry allows NO$_{\mathrm{x}}$ chemistry to involve reservoir species. Our study also emphasizes the need for accurate UV stellar spectra to understand the atmospheric chemistry of exoplanets., 20 pages, 14 figures, accepted for publication in MNRAS

Ultracool dwarfs comprise a significant proportion of stars in the Milky Way. Deep samples of UCDs have the potential to constrain the formation history and evolution of low-mass objects in the Galaxy, but well-characterized photometric and spectral samples have been limited to the local volume (d < 100 pc). Fortunately, the Vera Rubin Observatory will uncover UCDs throughout various environments in the Galaxy, and new tools are needed to analyze these data. We used a Monte-Carlo simulation-based tool to predict observable properties of UCDs such as kinematics, colors and number counts by modeling UCDs in distinct thin disk, thick and halo populations. We predict that >1 million M5—T9 UCDs, including >300,000 L dwarfs with and ~100 T dwarfs will be detectable with proper motion over 10 years., This poster was present at Coolstars22

LTT 1445 is a hierarchical triple M-dwarf star system located at a distance of 6.86 parsecs. The primary star LTT 1445A (0.257 M_Sun) is known to host the transiting planet LTT 1445Ab with an orbital period of 5.4 days, making it the second closest known transiting exoplanet system, and the closest one for which the host is an M dwarf. Using TESS data, we present the discovery of a second planet in the LTT 1445 system, with an orbital period of 3.1 days. We combine radial velocity measurements obtained from the five spectrographs ESPRESSO, HARPS, HIRES, MAROON-X, and PFS to establish that the new world also orbits LTT 1445A. We determine the mass and radius of LTT 1445Ab to be 2.87+/-0.25 M_Earth and 1.304^{+0.067}_{-0.060} R_Earth, consistent with an Earth-like composition. For the newly discovered LTT 1445Ac, we measure a mass of 1.54^{+0.20}_{-0.19} M_Earth and a minimum radius of 1.15 R_Earth, but we cannot determine the radius directly as the signal-to-noise of our light curve permits both grazing and non-grazing configurations. Using MEarth photometry and ground-based spectroscopy, we establish that star C (0.161 M_Sun) is likely the source of the 1.4-day rotation period, and star B (0.215 M_Sun) has a likely rotation period of 6.7 days. We estimate a probable rotation period of 85 days for LTT 1445A. Thus, this triple M-dwarf system appears to be in a special evolutionary stage where the most massive M dwarf has spun down, the intermediate mass M dwarf is in the process of spinning down, while the least massive stellar component has not yet begun to spin down., Comment: Accepted to the Astronomical Journal. 4 tables, 10 figures; RV table available upon request

Stellar activity poses one of the main obstacles for the detection and characterisation of exoplanets around cool stars, as it can induce radial velocity (RV) signals that can hide or mimic the presence of companions. Several activity indicators are routinely used to identify activity-related signals in RV measurements, but not all indicators trace exactly the same effects, nor are any of them always effective in all stars. In this work, we evaluate the performance of a set of common spectroscopic activity indicators for 98 M dwarfs observed with CARMENES. We find that different indicators behave differently depending on the mass and activity level of the target star. In addition, we also observe that stars at the low-mass end of the sample show the lowest RV scatter, which could potentially hint at different manifestations of activity compared to higher-mass stars, as well as being better candidates for planet searches. Overall, our results show that when assessing the origin of an RV signal, it is critical to take into account a large set of indicators, or at least the most effective ones considering the characteristics of the star, as failing to do so may lead to false planet claims.

I present an analysis of starspot modulation and flares in the TESS light curves of 112 M dwarfs with a TESS magnitude, {"references":["Stelzer, Beate et al. (2016). A path towards understanding the rotation-activity relation of M dwarfs with K2 mission, X-ray and UV data. MNRAS, 463, 1844","Raetz, Stefanie et al. (2020). Rotation-activity relations and flares of M dwarfs with K2 long- and short-cadence data. A&A, 637, A22","Hawley, Suzanne et al. (2014). Kepler Flares. I. Active and Inactive M Dwarfs. ApJ, 797, 121","Kaltenegger, L. et al. (2019). TESS Habitable Zone Star Catalog . ApJ, 874, L8"]}

We present the LHS 1678 (TOI-696) exoplanet system: two nearly Earth-sized transiting planets detected by TESS and a likely brown dwarf orbiting a bright M2 dwarf at 19.9 pc. The ultra-short-period LHS 1678 b (0.70 Earth radii, 0.9-day orbit) is a captivating target for emission spectroscopy observations with the JWST. LHS 1678 c (0.98 Earth radii, 3.7-day orbit) is in the Venus-zone and may be Venus density: a promising target for greenhouse effect studies. Both planets are favorable targets for EPRV mass measurements and for JWST transmission spectroscopy observations to study their atmospheres. The substellar companion, detected via CTIO/SMARTS 0.9m astrometry, is on a decades-long orbit and may someday eclipse the host star, revealing a rare system architecture in which more and less massive objects orbit in the same plane. There is also a candidate third planet detected in TESS multi-cycle data in near 4:3 resonance with LHS 1678 c. The host star is associated with an observed gap in the HR diagram tied to a change in M dwarf energy transport mechanisms. The effect of the associated stellar astrophysics on exoplanet evolution is currently unknown. In aggregate, LHS 1678 an exciting playground for comparative exoplanet science and understanding the formation and evolution of small, short-period exoplanets orbiting low-mass stars., {"references":["Astudillo-Defru, N., Forveille, T., Bonfils, X., et al. 2017b, A&A, 602, A88, doi: 10.1051/0004-6361/201630153","Baraffe, I., & Chabrier, G. 2018, A&A, 619, A177, doi: 10.1051/0004-6361/201834062","Benedict, G. F., Henry, T. J., Franz, O. G., et al. 2016, AJ, 152, 141, doi: 10.3847/0004-6256/152/5/141","Carter, J. A., & Agol, E. 2013, ApJ, 765, 132, doi: 10.1088/0004-637X/765/2/132","Chen, J., & Kipping, D. 2017, ApJ, 834, 17, doi: 10.3847/1538-4357/834/1/17","Cutri, R. M., Skrutskie, M. F., van Dyk, S., et al. 2003, 2MASS All 1671 Sky Catalog of point sources.","Engle, S. G., & Guinan, E. F. 2018, Research Notes of the American Astronomical Society, 2, 34, doi: 10.3847/2515-5172/aab1f8","Foreman-Mackey, D. 2018, Research Notes of the American Astronomical Society, 2, 31, doi: 10.3847/2515-5172/aaaf6c","Gaia Collaboration, Prusti, T., de Bruijne, J. H. J., et al. 2016, A&A, 595, A1, doi: 10.1051/0004-6361/201629272","Goldreich, P., & Schlichting, H. E. 2014, AJ, 147, 32, doi: 10.1088/0004-6256/147/2/32","Henry, T. J., Walkowicz, L. M., Barto, T. C., & Golimowski, D. A. 2002, AJ, 123, 2002, doi: 10.1086/339315","Hippke, M., & Heller, R. 2019a, A&A, 623, A39, doi: 10.1051/0004-6361/201834672","Huang, C. X., Vanderburg, A., Pál, A., et al. 2020a, Research 1754 Notes of the American Astronomical Society, 4, 204, doi: 10.3847/2515-5172/abca2e","Huang, C. X., Vanderburg, A., Pál, A., et al. 2020b, Research Notes of the American Astronomical Society, 1757 4, 206, doi: 10.3847/2515-5172/abca2d","Jao, W.-C., Henry, T. J., Gies, D. R., & Hambly, N. C. 2018, ApJL, 861, L11, doi: 10.3847/2041-8213/aacdf6","Jao, W.-C., Henry, T. J., Subasavage, J. P., et al. 2005, AJ, 129, 1954, doi: 10.1086/428489","Kempton, E. M. R., Bean, J. L., Louie, D. R., et al. 2018, PASP, 130, 114401, doi: 10.1088/1538-3873/aadf6f","Kostov, V. B., Mullally, S. E., Quintana, E. V., et al. 2019b, AJ, 157, 124, doi: 10.3847/1538-3881/ab0110","Kreidberg, L., Koll, D. D. B., Morley, C., et al. 2019, Nature, 573, 87, doi: 10.1038/s41586-019-1497-4","Kruse, E., Agol, E., Luger, R., & Foreman-Mackey, D. 2019, ApJS, 244, 11, doi: 10.3847/1538-4365/ab346b","Lightkurve Collaboration, Cardoso, J. V. d. M., Hedges, C., et al. 2018, Lightkurve: Kepler and TESS time series analysis in Python, Astrophysics Source Code Library. http://ascl.net/1812.013","Morton, T. D. 2015, VESPA: False positive probabilities calculator. http://ascl.net/1503.011","Newton, E. R., Irwin, J., Charbonneau, D., et al. 2017, ApJ, 834, 85, doi: 10.3847/1538-4357/834/1/85","Pepe, F. A., Cristiani, S., Rebolo Lopez, R., et al. 2010, in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, Vol. 7735, Ground-based and Airborne Instrumentation for Astronomy III, 77350F, doi: 10.1117/12.857122","Salvatier, J., Wiecki, T. V., & Fonnesbeck, C. 2016, PeerJ Computer Science, 2, e55","Suárez Mascareño, A., Faria, J. P., Figueira, P., et al. 2020, A&A, 639, A77, doi: 10.1051/0004-6361/202037745","Vanderburg, A., Latham, D. W., Buchhave, L. A., et al. 2016, ApJS, 222, 14, doi: 10.3847/0067-0049/222/1/14","Winters, J. G., Henry, T. J., Lurie, J. C., et al. 2015, AJ, 149, 5, doi: 10.1088/0004-6256/149/1/5","Zeng, L., Jacobsen, S. B., Sasselov, D. D., et al. 2019, Proceedings of the National Academy of Science, 116, 9723, doi: 10.1073/pnas.1812905116"]}

We present the confirmation of 2 planets around the M3 dwarf TOI-1468 at orbital periods of 1.88 and 15.53 days, one on each side of the radius valley, first detected by TESS and then confirmed by precise follow-up RV measurements with the CARMENES spectrograph., This is an interactive poster https://docs.google.com/presentation/d/1qT__Sx6Ae7fnWSy6mYOKsBjZtHE3RBN2LZ4hLbEBaAk/edit?usp=sharing

M dwarfs are key targets for high-resolution spectroscopic analyses due to a high incidence of these stars in the solar neighbourhood and their importance as exoplanetary hosts. Several methodological challenges make such analyses difficult, leading to significant discrepancies in the published results. We compare M dwarf parameters derived by recent high-resolution near-infrared studies with each other and with fundamental stellar parameters. We also assess to what extent deviations from local thermodynamic equilibrium (LTE) for Fe and K influence the outcome of these studies. We carry out line formation calculations based on a modern model atmosphere grid along with a synthetic spectrum synthesis code that treats formation of atomic and molecular lines in cool-star atmospheres including departures from LTE. We use near-infrared spectra collected with the CRIRES instrument at the ESO VLT as reference observational data. We find that the effective temperatures obtained by the different studies mostly agree to better than 100 K. We see a much worse agreement in the surface gravities and metallicities. We demonstrate that non-LTE effects are negligible for Fe I in M-dwarf atmospheres but are important for K I. These effects, leading to K abundance and metallicity corrections on the order of 0.2 dex, may be responsible for some of the discrepancies in the published analyses. Differences in the temperature-pressure structures of the atmospheric models may be another factor contributing to the discrepancies, in particular at low metallicities and high effective temperatures. In high-resolution spectroscopic studies of M dwarfs attention should be given to details of the line formation physics as well as input atomic and molecular data. Collecting high-quality, wide wavelength coverage spectra of benchmark M dwarfs is an essential future step., Comment: 20 pages, 11 figures. Accepted in A&A

Brown dwarfs are characterized by low masses that preclude the sustained hydrogen fusion characteristic of stars on the main sequence. Very cool, low mass M dwarfs are abundant within our galaxy and can be identified through various spectral features, such as the presence of TiO absorption bands. L dwarfs, though less common, are even cooler than M dwarfs, and are characterized by the presence of metallic hydrides in their spectra. We analyze the optical and infrared spectra of 42 M and L dwarfs, observed with the Magellan Echellette (MagE) optical spectrograph and Magellan infrared spectrometer FIRE in order to investigate the relationship between metallicity and galactic dynamics for these low mass objects. In particular, we examine whether older, higher metallicity objects have an increased galactic motion due to movement away from the galactic disk. We first look for evidence of this relationship within the two subsamples of M dwarfs and L dwarfs. We then compare the motions of the L Dwarfs and M dwarfs in our sample to see if the proposed metallicity-motion relationship provides kinematic evidence that M Dwarfs are older than L Dwarfs., {"references":["Gagne, Lambrides, Faherty, Simcoe. Firehose v2.0. Zenodo. 10.5281/zenodo.18775","Bochanski et al. 2009, PASP, 121, 1409B","Gaia Collaboration 2018, A&A, 616A, 1G","Allard, F. 2014, IAUS, 299, 271A","Burgasser et al. 2015, ApJS, 220, 18B","Dieterich et al. 2014, AJ, 147, 94D","Johnson & Soderblom 1987, AJ, 93, 864J","Mann et al. 2014, AJ, 147, 160","McLean et al. 2007, ApJ, 658, 1217M","Newton et al. 2014, AJ, 147, 20","Rojas-Ayala et al. 2012, ApJ, 748, 93"]}

High-energy particles from M-dwarf superflares--flares with energy\(\geq 10^{33}\) erg--can dramatically impact habitable-zone planets around these cool stars, with possible effects including the excitation of intense aurorae as particles interact with planetary atmospheres. Prior work has demonstrated that Earthlike atmospheres can produce excess emission in M-dwarf spectra, with the star/planet contrast ratio increasing by orders of magnitude in the green 5577-Å auroral line to levels potentially detectable by future surveys. The Evryscopes are gigapixel-scale telescope arrays at Mount Laguna Observatory and Cerro-Tololo Inter-American Observatory; coupled with the Evryscope Fast Transient Engine (EFTE), which scans Evryscope images in real time for transient phenomena, the systems have the unprecedented ability to identify superflares across the entire sky as they begin, enabling rapid spectroscopic follow-up. With the Evryscopes' all-sky coverage, far more--and far brighter--flares are observable than in surveys that focus on individual targets. Using the Goodman spectrograph on the 4.1-m SOAR telescope, we follow the spectroscopic evolution of M-dwarf superflares as they happen. Preliminary results include the strongest-yet upper limits to be placed on auroral emission in the atmospheres of Earthlike planets orbiting M-dwarf stars.

Comprising three out of every four stars, the M dwarfs form a unique sample that can host companions orbiting at Solar System scales and spanning a factor of 100,000 in mass. Targeting 120 M dwarf binaries within 25 parsecs, we are determining the period vs. eccentricity distribution for M dwarf stellar companions with orbital periods up to 6 years and semimajor axes up to 5 AU. This range is enabled by our combination of multiple observational methods: long-term astrometry from our RECONS program at the CTIO/SMARTS 0.9m is characterizing orbits on decades-long timescales, while our speckle interferometry survey at SOAR with HRCAM+SAM maps shorter orbits of systems identified from Gaia DR2, while also providing resolutions and masses for our long-period astrometric binaries. We will supplement these results with orbits from the literature, from both radial velocity and high-resolution imaging surveys, to ensure that our sample is rich with companions of all types orbiting within 5 AU. Initial results of this work so far suggest a notable paucity of M dwarf stellar companions with circular orbits greater than 5 years in period, showcasing the additional leverage provided by this combination of long-term astrometry and high-resolution imaging. Ultimately, when compared to the orbits of brown dwarf and planetary companions, such structures will be critical to understanding the formation mechanisms of these systems., {"references":["Bate, M. 2015, Living Together: Planets, Host Stars and Binaries, 496, 37","Dupuy & Liu 2017, ApJS, 231, 15","Raghavan, D., McAlister, H., Henry, T., et al. 2010, ApJS, 190, 1","Tokovinin, A., Cantarutti, R., Tighe, R., et al 2016, PASP, 128, 125003"]}

Mt. Abu Faint Object Spectrograph and Camera (MFOSC-P) is an in-house developed instrument for Physical Research Laboratory (PRL) 1.2m telescope at Mt. Abu India, commissioned in February 2019. Here we present the first science results derived from the low resolution spectroscopy program of a sample of M Dwarfs carried out during the commissioning run of MFOSC-P between February-June 2019. M dwarfs carry great significance for exoplanets searches in habitable zone and are among the promising candidates for the observatory's several ongoing observational campaigns. Determination of their accurate atmospheric properties and fundamental parameters is essential to constrain both their atmospheric and evolutionary models. In this study, we provide a low resolution (R$\sim$500) spectroscopic catalogue of 80 bright M dwarfs (J$, Comment: Accepted for Publication in MNRAS

Context. Planets orbiting low-mass stars such as M dwarfs are now considered a cornerstone in the search for life-harbouring planets. GJ 273 is a planetary system orbiting an M dwarf only 3.75 pc away, composed of two confirmed planets, GJ 273b and GJ 273c, and two promising candidates, GJ 273d and GJ 273e. Planet GJ 273b resides in the habitable zone. Currently, due to a lack of observed planetary transits, only the minimum masses of the planets are known: Mb sin ib=2.89 M⊕, Mc sin ic=1.18 M⊕, Md sin id=10.80 M⊕, and Me sin ie=9.30 M⊕. Despite being an interesting system, the GJ 273 planetary system is still poorly studied. Aims. We aim at precisely determine the physical parameters of the individual planets, in particular to break the mass–inclination degeneracy to accurately determine the mass of the planets. Moreover, we present thorough characterisation of planet GJ 273b in terms of its potential habitability. Methods. First, we explored the planetary formation and hydration phases of GJ 273 during the first 100 Myr. Secondly, we analysed the stability of the system by considering both the two- and four-planet configurations. We then performed a comparative analysis between GJ 273 and the Solar System, and searched for regions in GJ 273 which may harbour minor bodies in stable orbits, i.e. main asteroid belt and Kuiper belt analogues. Results. From our set of dynamical studies, we obtain that the four-planet configuration of the system allows us to break the mass– inclination degeneracy. From our modelling results, the masses of the planets are unveiled as: 2:89 ≤ Mb ≤ 3:03 M⊕, 1:18 ≤ Mc ≤ 1:24 M⊕, 10:80 ≤ Md ≤ 11:35 M⊕ and 9:30 ≤ Me ≤ 9:70 M⊕. These results point to a system likely composed of an Earth-mass planet, a super-Earth and two mini-Neptunes. From planetary formation models, we determine that GJ 273b was likely an efficient water captor while GJ 273c is probably a dry planet. We found that the system may have several stable regions where minor bodies might reside. Collectively, these results are used to comprehensively discuss the habitability of GJ 273b, Spanish Ministry of Science and Education Ramón y Cajal programme ESP2017-87676-2-2 RYC-2012-09913, CONICYT- FONDECYT/Chile Postdoctorado 3180405, MIT’s Kavli Institute

This contributed poster was given in the poster session at the 20th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun (Cool Stars 20) in July 2018., Chang et al. in preparation (2018) soon to be submitted to PASA.

We present an analysis of high-resolution spectropolarimetric observations of the active M dwarf AD Leo in all four Stokes parameters. We derived the least-squares deconvolved Stokes profiles and detected linear polarisation signatures in spectral lines. This is the first report of a detection of Zeeman linear polarisation in the spectral lines of an M dwarf. Simultaneously, we discovered that the circular polarisation profiles corresponding to our data set are significantly weaker and broader than those present in all archival spectra of AD Leo, which exhibited approximately constant profiles over the period 2006–2012. Magnetic maps obtained using Zeeman Doppler imaging confirm a significant - and apparently rather sudden - change in the surface magnetic field. On the one hand, the topology of the magnetic field is mostly unchanged and remains close to an axisymmetric dipole. On the other hand, the total energy of the large-scale magnetic field has decreased by about 20 percent between 2012 and 2016 and the filling factor of this component has decreased by about a factor of two. These results suggest that the field responsible for the observed circular polarisation signatures corresponds to a stronger field component occupying a smaller fraction of the stellar surface in the more recent map. These results represent the first evidence that an active M dwarf with dipole-dominated axisymmetric field topology can undergo a long-term global magnetic field evolution.

The presence and strength of stellar magnetic activity is rooted in a star's fundamental parameters such as mass and age. Age-resolved investigations of chromospheric activity indicators, and large scale magnetic field observations suggest that one can access an individual star's age via its magnetic activity. Can flares, magnetically driven energetic outbursts of energy on the surfaces of stars, serve as an accurate stellar clock" then? For a star with given mass, the probability to encounter a flare scales as a power law with its total released energy. If there is an activity-age relation in the form of a flaring-age relation we expect the observed flaring rates and energies to vary significantly in these objects. Thus, the slope and intercept of the power law fit to the flare frequency distribution would be a function of both mass and age. The Kepler mission provides the means to test this hypothesis - high precision time domain photometry of thousands of stars in more than 10 open clusters spanning a wide range of ages. Using Kepler's K2 Campaigns 4 and 5 we explore the possibility to calibrate such a clock on the example of three open clusters: M67 (4.3 Gyr), M44 (0.63 Gyr) and the Pleiades (0.125 Gyr), and present first results., Poster number 143, {"references":["Aigrain et al. (2016), MNRAS 459, 2408-2419","Davenport (2016), ApJ 829, 23","Howell et al. (2014), PASP 126, 398-408","Skumanich (1972), ApJ 171, 565","Bell et al. (2012), MNRAS 424, 3178-91","Boudreault et al. (2012), MNRAS 426, 3419-34","Dias et al. (2012), A&A 539, A125","Netopil et al. (2016), A&A 585, A150","Rebull et al. (2016), AJ 152, 113","Kraus & Hillenbrand (2007), AJ 134, 2340-52","Douglas et al. (2017), ApJ 842, 83","Gonzalez (2016), MNRAS 459, 1060-68"]}

The Cannon (Ness et al. 2015)is a flexible, data-driven spectral modeling and parameter inference framework, demonstrated on high-resolution Apache Point Galactic Evolution Experiment (APOGEE; λ/Δλ~22,500, 1.5-1.7µm) spectra of giant stars to estimate stellar labels (Teff, logg, [Fe/H], and chemical abundances) to precisions higher than the model-grid pipeline. The lack of reliable stellar parameters reported by the APOGEE pipeline for temperatures less than ~3550K (Schmidt et al. 2016), motivates the extension of this approach to M dwarf stars. Using a training set of 51 M dwarfs with spectral types ranging M0-M9 obtained from SDSS optical spectra, we demonstrate that The Cannon can infer spectral types to a precision of 0.6 types. We then use 30 M dwarfs ranging 3072 < Teff < 4131K, and -0.48 < [Fe/H] < 0.49 to train a two-parameter model precise to 44K and 0.05 dex respectively. Additionally we discuss the extension of a model to other labels, and the scientific objectives a data-driven pipeline could enable.

The design and construction of CARMENES has been presented at previous SPIE conferences. It is a next-generation radial-velocity instrument at the 3.5m telescope of the Calar Alto Observatory, which was built by a consortium of eleven Spanish and German institutions. CARMENES consists of two separate échelle spectrographs covering the wavelength range from 0.52 to 1.71¿m at a spec-tral resolution of R < 80,000, fed by fibers from the Cassegrain focus of the telescope. CARMENES saw ¿First Light¿ on Nov 9, 2015. During the commissioning and initial operation phases, we established basic performance data such as throughput and spectral resolution. We found that our hollow-cathode lamps are suitable for precise wavelength calibration, but their spectra contain a number of lines of neon or argon that are so bright that the lamps cannot be used in simultaneous exposures with stars. We have therefore adopted a calibration procedure that uses simultaneous star / Fabry Pérot etalon exposures in combination with a cross-calibration between the etalons and hollow-cathode lamps during daytime. With this strategy it has been possible to achieve 1-2 m/s precision in the visible and 5-10 m/s precision in the near-IR; further improvements are expected from ongoing work on temperature control, calibration procedures and data reduction. Comparing the RV precision achieved in different wavelength bands, we find a ¿sweet spot¿ between 0.7 and 0.8¿m, where deep TiO bands provide rich RV information in mid-M dwarfs. This is in contrast to our pre-survey models, which predicted comparatively better performance in the near-IR around 1¿m, and explains in part why our near-IR RVs do not reach the same precision level as those taken with the visible spectrograph. We are now conducting a large survey of 340 nearby M dwarfs (with an average distance of only 12pc), with the goal of finding terrestrial planets in their habitable zones. We have detected the signatures of several previously known or suspected planets and also discovered several new planets. We find that the radial velocity periodograms of many M dwarfs show several significant peaks. The development of robust methods to distinguish planet signatures from activity-induced radial velocity jitter is therefore among our priorities. Due to its large wavelength coverage, the CARMENES survey is generating a unique data set for studies of M star atmospheres, rotation, and activity. The spectra cover important diagnostic lines for activity (H alpha, Na I D1 and D2, and the Ca II infrared triplet), as well as FeH lines, from which the magnetic field can be inferred. Correlating the time series of these features with each other, and with wavelength-dependent radial velocities, provides excellent handles for the discrimination between planetary companions and stellar radial velocity jitter. These data are also generating new insight into the physical properties of M dwarf atmospheres, and the impact of activity and flares on the habitability of M star planets. © 2018 SPIE., CARMENES is an instrument for the Centro Astronomico Hispano-Aleman de Calar Alto (CAHA, Almeria, Spain). CARMENES is funded by the German Max-Planck-Gesellschaft (MPG), the Spanish Consejo Superior de Investigaciones Cientificas (CSIC), the European Union through FEDER/ERF FICTS-2011-02 funds, and the members of the CARMENES Consortium (Max-Planck-Institut fur Astronomie, Instituto de Astrofisica de Andalucia, Landessternwarte Konigstuhl, Institut de Ciencies de l'Espai, Insitut fur Astrophysik Gottingen, Universidad Complutense de Madrid, Thuringer Landessternwarte Tautenburg, Instituto de Astrofisica de Canarias, Hamburger Sternwarte, Centro de Astrobiologia and Centro Astronomico Hispano-Aleman), with additional contributions by the Spanish Ministry of Science, the German Science Foundation through the Major Research Instrumentation Program and DFG Research Unit FOR2544 "Blue Planets around Red Stars", the Klaus Tschira Stiftung, the states of Baden-Wurttemberg and Niedersachsen, and by the Junta de Andalucia.

The Kepler mission has revealed that Earth-sized planets are common, and dozens have been discovered to orbit in or near their host star's habitable zone. A major focus in astronomy is to determine which of these exoplanets are likely to have Earth-like properties that are amenable to follow-up with both ground- and future space-based surveys, with an ultimate goal of probing their atmospheres to look for signs of life. Venus-like atmospheres will be of particular interest in these surveys. While Earth and Venus evolved to have similar sizes and densities, it remains unclear what factors led to the dramatic divergence of their atmospheres. Studying analogs to both Earth and Venus can thus shed light on the limits of habitability and the potential for life on known exoplanets. Here we present the discovery and confirmation of Kepler-1649b, an Earth-sized planet orbiting a nearby M5V star that receives incident flux at a level similar to that of Venus. We present our methods for characterizing the star, using a combination of PSF photometry, ground-based spectroscopy and imaging, to confirm the planetary nature of Kepler-1649b. Planets like Kepler-1649b will be prime candidates for atmospheric and habitability studies in the next generation of space missions., 8 pages, 9 figures

The aim of this thesis is to use a cross-match between WISE, 2MASS and SDSS to identify a large sample of M dwarfs. Through the careful characterisation and quality control of these M dwarfs I aim to identify rare systems (i.e. unresolved UCD companions, young M dwarfs, late M dwarfs and M dwarfs with common proper motion companions). Locating ultracool companions to M dwarfs is important for constraining low-mass formation models, the measurement of substellar dynamical masses and radii, and for testing ultracool evolutionary models. This is done by using an optimised method for identifying M dwarfs which may have unresolved ultracool companions. To do this I construct a catalogue of 440 694 M dwarf candidates, from WISE, 2MASS and SDSS, based on optical- and near-infrared colours and reduced proper motion. With strict reddening, photometric and quality constraints I isolate a sub-sample of 36 898 M dwarfs and search for possible mid-infrared M dwarf + ultracool dwarf candidates by comparing M dwarfs which have similar optical/near-infrared colours (chosen for their sensitivity to effective temperature and metallicity). I present 1 082 M dwarf + ultracool dwarf candidates for follow-up. Using simulated ultracool dwarf companions to M dwarfs, I estimate that the occurrence of unresolved ultracool companions amongst my M dwarf + ultracool dwarf candidates should be at least four times the average for my full M dwarf catalogue. I discuss yields of candidates based on my simulations. The possible contamination and bias from misidentified M dwarfs is then discussed, from chance alignments with other M dwarfs and UCDs, from chance alignments with giant stars, from chance alignments with galaxies, and from blended systems (via visual inspection). I then use optical spectra from LAMOST to spectral type a subset of my M dwarf + ultracool dwarf candidates. These candidates need confirming as true M dwarf + ultracool dwarf systems thus I present a new method I developed to use low resolution near-infrared spectra which relies on two colour similar objects (one an excess candidate, one not) having very similar spectra. A spectral difference of these two colour similar objects should leave the signature of a UCD in the residual of their differences, which I look for using the difference in two spectral bands designed to identify UCD spectral features. I then present the methods used to identify other rare systems from my full M dwarf catalogue. Young M dwarfs were identified by measuring equivalent widths of Hα from the LAMOST spectra, and by measuring rotation periods from Kepler 2 light curves. I identify late M dwarfs photometrically (using reduced proper motion and colour cuts) and spectroscopically (using the LAMOST spectra with spectral indices from the literature). Also I present common proper motion analysis aimed at finding Tycho-2 primaries for my M dwarfs and look for physically separated M dwarf + M dwarf pairs (internally within my full M dwarf catalogue).

YMGs are benchmarks for the transition of stellar populations from their birth clusters to the field. We present data and analysis from our Magellan Adaptive Optics (MagAO) campaign to image more than 100 M-dwarf members of several YMGs in the southern sky, revealing ~30 previously unresolved visual stellar companions at separations of ~3 — 500 AU. Our study provides multiplicity statistics for young M-dwarfs in this intermediate regime of orbital distance. We combine our results with the SACY survey (Elliott et al. 2015), whose focus is on YMG systems with earlier type primaries, to provide an updated measurement of multiplicity as a function of stellar mass with significantly more statistical power at lower masses. Additionally, the tighter systems in our sample provide the opportunity for future monitoring and dynamical mass inference.&nbsp

Context. M dwarfs are considered ideal targets for Doppler radial velocity searches. Nonetheless, the statistics of frequency of low-mass planets hosted by low mass stars remains poorly constrained. Aims. Our M-dwarf radial velocity monitoring with HARPS-N can provide a major contribution to the widening of the current statistics through the in-depth analysis of accurate radial velocity observations in a narrow range of spectral sub-types (79 stars, between dM0 to dM3). Spectral accuracy will enable us to reach the precision needed to detect small planets with a few earth masses. Our survey will bring a contribute to the surveys devoted to the search for planets around M-dwarfs, mainly focused on the M-dwarf population of the northern emisphere, for which we will provide an estimate of the planet occurence. Methods. We present here a long duration radial velocity monitoring of the M1 dwarf star GJ 3998 with HARPS-N to identify periodic signals in the data. Almost simultaneous photometric observations were carried out within the APACHE and EXORAP programs to characterize the stellar activity and to distinguish from the periodic signals those due to activity and to the presence of planetary companions. Results. The radial velocities have a dispersion in excess of their internal errors due to at least four superimposed signals, with periods of 30.7, 13.7, 42.5 and 2.65 days. The analysis of spectral indices based on Ca II H & K and Halpha lines demonstrates that the periods of 30.7 and 42.5 days are due to chromospheric inhomogeneities modulated by stellar rotation and differential rotation. The shorter periods of 13.74 +/- 0.02 d and 2.6498 +/- 0.0008 d are well explained with the presence of two planets, with minimum masses of 6.26 +/- 0.79 MEarth and 2.47 +/- 0.27 MEarth and distances of 0.089 AU and 0.029 AU from the host, respectively., 19 pages, 14 figures. Accepted for publication in Astronomy & Astrophysics

I examined the outlier variable objects in the field stars of the MEarth transit survey data set. I define an outlier as a field star with variance outside three standard deviations of the mean root-mean-square errors associated with its respective magnitude. The MEarth Project collects data from M dwarf stars, creating a survey of these small objects in search of exoplanets. I wrote a Python program which looked through this data set, and of 2149 fields examined, 578081 objects were found, and of those, 1004 had periods of statistical significance, or 0.17%. My program analyzes the root-mean-square residual of a star to determine if it has particularly high variance given its magnitude. Of these outlier stars, I estimated the best-fitting period for the observed flux using phase dispersion minimization (PDM), and phase-folded light curves. I compiled these stars into a list with basic parameters, such as RA, dec, J-, H-, and K-band magnitudes, and their periods, then I further investigated three by using the SIMBAD Astronomical Database to learn and catalogue their properties.

Kepler-296 is a binary star system with two M-dwarf components separated by 0.2 arcsec. Five transiting planets have been confirmed to be associated with the Kepler-296 system; given the evidence to date, however, the planets could in principle orbit either star. This ambiguity has made it difficult to constrain both the orbital and physical properties of the planets. Using both statistical and analytical arguments, this paper shows that all five planets are highly likely to orbit the primary star in this system. We performed a Markov-Chain Monte Carlo simulation using a five transiting planet model, leaving the stellar density and dilution with uniform priors. Using importance sampling, we compared the model probabilities under the priors of the planets orbiting either the brighter or the fainter component of the binary. A model where the planets orbit the brighter component, Kepler-296A, is strongly preferred by the data. Combined with our assertion that all five planets orbit the same star, the two outer planets in the system, Kepler-296 Ae and Kepler-296 Af, have radii of 1.53 +/- 0.26 and 1.80 +/- 0.31 R_earth, respectively, and receive incident stellar fluxes of 1.40 +/- 0.23 and 0.62 +/- 0.10 times the incident flux the Earth receives from the Sun. This level of irradiation places both planets within or close to the circumstellar habitable zone of their parent star., Comment: Accepted for publication in ApJ

Since the first detection of an extrasolar planet orbiting a Sun-like star by Mayor and Queloz (1995), more than 1500 have been discovered. Enormous interest is currently focused on finding and characterising Earth-like planets, in particular those located in the habitable zone of their host star (defined as the distance from the host star where the planet temperature allows liquid water to flow on its surface). Both the detection of Earth-like planets, and the search for biomarkers in their atmospheres are among the main objectives of the twenty-first century's astronomy. The method known as radial velocities (RV), that consists in the measure of the star's reflex motion induced by orbiting planets, is a promising technique to achieve that quest.The main difficulties with the RV technique are the needs of an extremely stable spectrograph, a correct understanding of stellar activity (which can mimic the effect of a planet), a careful treatment of our Earth's atmosphere (which inevitable imprints spectra taken from the ground), and the need to dispose of a powerful algorithm to extract as much Doppler information as possible from the recorded spectra. Search for planets orbiting very low-mass stars (M dwarfs) can more easily reach the goal of detecting low-mass planets in the habitable zone of their parent star, compared to solar-type stars. Indeed, everything else being equal, a lower mass of the host star implies a larger reflex motion, and thus a larger RV amplitude. Moreover, the lower luminosity of M dwarfs compared to Sun-like stars, implies shorter orbital periods from planets in the habitable zone (~50 days against ~360 days, for M dwarfs compared to solar-type stars, respectively), resulting again in a larger RV amplitude. A RV precision of ~1 m/s allows a planet detection in the habitable zone of an M dwarf, whereas ~0.1 m/s is required in the case of a solar-type stars.This thesis aims to optimise the RV extraction from HARPS high-resolution spectra (and to open similar analysis on other instruments like SOPHIE, HARPS-N and the upcoming infrared spectrograph SPIRou -- to be commissioned to the 3.6-m CFH-Telescope). The effects of stellar activity will also be analysed, and contextualised in the RV technique. Stellar activity tracers are used to reject false detections or to study the relationships between the stellar magnetic activity and rotation. In this thesis (Chap.ref{chap:mag_activity}) I calibrate for the first time the ratio between the Ca textrm{small II} Htextrm{small &}K chromospheric lines and the bolometric luminosity for M dwarfs. I determine a relationship between the R^prime_{HK}-index and the rotation period of M dwarfs. In chapter~ref{chap:template_matching} I describe my algorithm to extract RVs through a chi^2-minimisation between a stellar template and the observed spectra. I demonstrate the improved accuracy of this method. Telluric spectral lines also affect the measurements of RV and are taken into account in the analysis procedures. I tested these methods on systems with planetary candidates, and for some systems, I took in charge the Keplerian analysis., Depuis la première détection d'une planète extrasolaire autour d'une étoile de type solaire par Mayor et Queloz (1995), plus de 1500 planètes ont été découverts. Actuellement il existe un énorme intérêt à découvrir et caractériser des planètes semblables à la Terre, en particulier celles situées dans la zone habitable de leur étoile hôte (définie comme la distance à l'étoile hôte où la température de la planète permet l'existence d'eau liquide à la surface). La détection de planètes de type terrestre, et la recherche de biomarqueurs dans leurs atmosphères sont parmi les principaux objectifs de l'astronomie du vingt et unième siècle. La méthode des vitesses radiales (VR), consistant à mesurer le mouvement réflexe de l'étoile induit par des planètes en orbite, est une remarquable technique pour atteindre cet objectif.Pour atteindre les précisions nécessaire à la detection de telles planètes il est absolument nécessaire de concevoir des spectrographes extrêmement stables, d'avoir une très bonne compréhension de l'activité stellaire (qui peut mimer l'effet d'une planète), d'effectuer un traitement soigneux de l'atmosphère terrestre (laquelle inévitablement laisse des empreintes dans les spectres acquis depuis le sol), et de disposer d'une puissante technique pour extraire, à partir des spectres, autant d'information Doppler que possible. La recherche de planètes orbitant autour des étoiles de très faible masse, plutôt qu'autour des étoiles de type solaire, permet d'aborder dès maintenant la détection de planètes de faible masse dans la zone habitable. En effet, en gardant tout les autres paramètres égaux, le mouvement réflexe (et donc l'amplitude de la variation VR) sera plus grande si l'étoile centrale est de très faible masse. De plus les naines M ont une plus faible luminosité que les étoiles de type solaire, il en resulte des périodes orbitales courtes des planètes dans la zone habitable (~50 jours pour les naines M contre ~360 jours pour des étoiles de type solaire), entraînant à nouveau en une plus grande amplitude des VR. Une précision de ~1 m/s en VR permet la détection d'une planète dans la zone habitable d'une naine M, alors que ~0.1 m/s sont nécessaire dans le cas d'une étoile de type solaire.Cette thèse vise à optimiser l'extraction de VR des spectres des naines M à haute résolution acquis avec le spectrographe HARPS (avec une possibilité d'applications futures sur d'autres instruments comme SOPHIE, HARPS-N et le prochain spectrographe infrarouge SPIRou - prochainement mis en service au CFHT). Les effets de l'activité stellaire des naines M seront également analysées, dans le contexte de la technique des VR. Divers traceurs d'activité stellaire sont utilisés pour rejeter des fausses détections ou pour étudier les relations entre l'activité magnétique et la rotation. Dans cette thèse (Chap. 3) je calibre pour la première fois le flux dans les raies H et K du Calcium en fonction de la luminosité bolométrique et je détermine la relation entre cet estimateur R'HK et la période de rotation des naines M. Dans le chapitre 4 je décris l'implémentation d'une méthode d'extraction de VR par une minimisation du Chi-deux entre un template spectral et les spectres observés. Je démontre que cette méthode est plus précise que celle classiquement utilisée. Les raies telluriques qui affectent les mesures VR sont prises en compte dans les procédures d'analyse. Ces méthodes sont testées sur des systèmes avec des candidats planétaires, je discuterais l'analyse de certains de ces systèmes.