Photospheric properties and fundamental parameters of M dwarfs

M dwarfs are an important source of information when studying and probing the lower end of the Hertzsprung-Russell (HR) diagram, down to the hydrogen-burning limit. Being the most numerous and oldest stars in the galaxy, they carry fundamental information on its chemical history. The presence of molecules in their atmospheres, along with various condensed species, complicates our understanding of their physical properties and thus makes the determination of their fundamental stellar parameters more challenging and difficult. The aim of this study is to perform a detailed spectroscopic analysis of the high-resolution H-band spectra of M dwarfs in order to determine their fundamental stellar parameters and to validate atmospheric models. The present study will also help us to understand various processes, including dust formation and depletion of metals onto dust grains in M dwarf atmospheres. The high spectral resolution also provides a unique opportunity to constrain other chemical and physical processes that occur in a cool atmosphere The high-resolution APOGEE spectra of M dwarfs, covering the entire H-band, provide a unique opportunity to measure their fundamental parameters. We have performed a detailed spectral synthesis by comparing these high-resolution H-band spectra to that of the most recent BT-settl model and have obtained fundamental parameters such as effective temperature, surface gravity, and metallicity (Teff, log g and [Fe/H]) respectively.Comment: 15 pages, 10 figures, accepted for publication in A&

Progress in Modeling Very Low Mass Stars, Brown Dwarfs, and Planetary Mass Objects

We review recent advancements in modeling the stellar to substellar transition. The revised molecular opacities, solar oxygen abundances and cloud models allow to reproduce the photometric and spectroscopic properties of this transition to a degree never achieved before, but problems remain in the important M-L transition characteristic of the effective temperature range of characterizable exoplanets. We discuss of the validity of these classical models. We also present new preliminary global Radiation HydroDynamical M dwarfs simulations.Comment: Submitted to Mem. S. A. It. Supp

Detection and characterisation of two VLM binaries: LP 1033-31 and LP 877-72

Using the high-resolution near-infrared adaptive optics imaging from the NaCo instrument at the Very Large Telescope, we report the discovery of a new binary companion to the M-dwarf LP 1033-31 and also confirm the binarity of LP 877-72. We have characterised both the stellar systems and estimated the properties of their individual components. We have found that LP 1033-31 AB with the spectral type of M4.5+M4.5 has a projected separation of 6.7$\pm$1.3 AU. Whereas with the spectral type of M1+M4, the projected separation of LP 877-72 AB is estimated to be 45.8$\pm$0.3 AU. The binary companions of LP 1033-31 AB are found to have similar masses, radii, effective temperatures, and log $g$ with the estimated values of 0.20$\pm$0.04 $\rm{M}_{\odot}$, 0.22$\pm$0.03 $\rm{R}_{\odot}$, 3200 K, 5.06$\pm$0.04. However, the primary of LP 877-72 AB is found to be twice as massive as the secondary with the derived mass of 0.520$\pm$0.006 $\rm{M}_{\odot}$. The radius and log $g$ for the primary of LP 877-72 AB are found to be 1.8 and 0.95 times that of the secondary component with the estimated values of 0.492$\pm$0.011 $\rm{R}_{\odot}$ and 4.768$\pm$0.005, respectively. With an effective temperature of 3750$\pm$15 K, the primary of LP 877-72 AB is also estimated to be $\sim$400 K hotter than the secondary component. We have also estimated the orbital period of LP 1033-31 and LP 877-72 to be $\sim$28 and $\sim$349 yr, respectively. The binding energies for both systems are found to be $\gt$10$^{43}$ erg, which signifies both systems are stable.Comment: 14 pages, 6 figures, accepted for publication in MNRA

A high resolution spectroscopic atlas of M subdwarfs - Effective temperature and metallicity

Context. M subdwarfs are metal poor and cool stars. They are important probes of the old galactic populations. However, they remain elusive due to their low luminosity. Observational and modeling efforts are required to fully understand their physics and to investigate the effects of metallicity in their cool atmospheres. Aims. We perform a detailed study of a sample of subdwarfs to determine their stellar parameters and constrain the stat-of-the art atmospheric models. Methods. We present UVES/VLT high resolution spectra of three late-K subdwarfs and 18 M subdwarfs. Our atlas covers the optical region from 6400 AA up to the near infrared at 8900 AA. We show spectral details of cool atmospheres at very high resolution (R= 40 000) and compare with synthetic spectra computed from the recent BT-Settl atmosphere models. Results. Our comparison shows that molecular features (TiO, VO, CaH), and atomic features (Fe I, Ti I, Na I, K I) are well fitted by current models. We produce an effective temperature versus spectral type relation all over the subdwarf spectral sequence. Thanks to the high resolution of our spectra, we perform a detailed comparison of line profiles of individual elements such as Fe I, Ca II, Ti I, and are able to determine accurate metallicities of these stars. These determinations contribute to calibrate the relation between metallicity and molecular band strength indices from low-resolution spectra. Conclusions. This work shows that the new generation of models are able to reproduce various spectral features of M subdwarfs. Working with these high resolution spectra allowed us to disentangle the atmospheric parameters (effective temperature, gravity, metallicity), which is not possible when using low resolution spectroscopy or photometry.Comment: 15 pages, 20 figures, 2 tables, accepted for publication in Astronomy and Astrophysic

IN VITRO ANTIOXIDANT, ANTIMICROBIAL AND ADMET STUDY OF NOVEL FURAN/BENZOFURAN C-2 COUPLED QUINOLINE HYBRIDS

Objectives: Synthesis of novel 2-(benzofuran-2-yl) and 2-(furan-2-yl) quinoline-4- carboxylates and their [2-(1-benzofuran-2-yl) quinolin-4-yl] methanol, [2-(1-furan-2-yl) quinolin-4-yl] methanol and its derivatives for antioxidant, antimicrobial and ADMET study.Methods: Synthesis was carried with conventional method and the structures were confirmed by IR, 1H NMR, 13C NMR and mass spectral analysis. The antioxidant activity was performed by DPPH and H2O2 radical scavenging method. Antimicrobial investigation was established by cup plate and food poison technique. The in silico absorption, distribution, metabolism, excretion and toxicity (ADMET) study of the drug was carried out in ACD/lab-2.Results: The antioxidant activity results revealed that, compounds 4b-c, 5a-b, 10c and 10f exhibited good DPPH radical and hydrogen peroxide scavenging activity. The antibacterial results revealed that, compounds 4c, 5a-b, 10b, 10d and 10f exhibited good activity against Escherichia coli, Klebsiella pneumonia and Salmonella typhimurium. Further, the antifungal activity results showed that, compounds 4c, 5c and 10c-e were showing good activity against Aspergillus flavus and Candida neoformans.  The mean value of P<0.05 were considered to be statistically significant. The ADMET results revealed that compounds emerged as a potential candidate for antioxidant and antimicrobial agents.Conclusion: The study reveals that compounds containing furan/benzofuran coupled heterocycles are play the important role for activity as they possess potent antioxidant and antimicrobial agents. The in silico ADME analysis also suggesting the compounds were in acceptable range to obey the pharmacokinetic parameters.Â

The effective temperature scale of M dwarfs

Context. Despite their large number in the Galaxy, M dwarfs remain elusive objects and the modeling of their photosphere has long remained a challenge (molecular opacities, dust cloud formation). Aims. Our objectives are to validate the BT-Settl model at

First Results from MFOSC-P : Low Resolution Optical Spectroscopy of a Sample of M dwarfs within 100 parsecs

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$500) spectroscopic catalogue of 80 bright M dwarfs (J$<$10) and classify them using their optical spectra. We have also performed the spectral synthesis and $\chi^2$ minimisation techniques to determine their fundamental parameters viz. effective temperature and surface gravity by comparing the observed spectra with the most recent BT-Settl synthetic spectra. Spectral type of M dwarfs in our sample ranges from M0 to M5. The derived effective temperature and surface gravity are ranging from 4000 K to 3000 K and 4.5 to 5.5 dex, respectively. In most of the cases, the derived spectral types are in good agreement with previously assigned photometric classification.Comment: Accepted for Publication in MNRA

The Effective Temperature Scale of M dwarfs

Despite their large number in the Galaxy, M dwarfs remain elusive objects and the modeling of their photospheres has long remained a challenge (molecular opacities, dust cloud formation). Our objectives are to validate the BT-Settl model atmospheres, update the M dwarf T eff -spectral type relation, and find the atmospheric parameters of the stars in our sample. We compare two samples of optical spectra covering the whole M dwarf sequence with the most recent BT-Settl synthetic spectra and use a \c{hi}2 minimization technique to determine Teff . The first sample consists of 97 low-resolution spectra obtained with NTT at La Silla Observatory. The second sample contains 55 mid-resolution spectra obtained at the Siding Spring Observatory (SSO). The spectral typing is realized by comparison with already classified M dwarfs. We show that the BT-Settl synthetic spectra reproduce the slope of the spectral energy distribution and most of its features. Only the CaOH band at 5570{\AA} and AlH and NaH hydrides in the blue part of the spectra are still missing in the models. The Teff-scale obtained with the higher resolved SSO 2.3 m spectra is consistent with that obtained with the NTT spectra. We compare our Teff scale with those of other authors and to published isochrones using the BT-Settl colors. We also present relations between effective temperature, spectral type and colors of the M dwarfs.Comment: 16 pages, 6 figures, accepted for publication in A&

Deep Low-frequency Radio Observations of A2256. I. the Filamentary Radio Relic

We present deep and high-fidelity images of the merging galaxy cluster A2256 at low frequencies using the upgraded Giant Metrewave Radio Telescope (uGMRT) and LOw-Frequency ARray (LOFAR). This cluster hosts one of the most prominent known relics with a remarkably spectacular network of filamentary substructures. The new uGMRT (300-850 MHz) and LOFAR (120-169 MHz) observations, combined with the archival Karl G. Jansky Very Large Array (VLA; 1-4 GHz) data, allowed us to carry out the first spatially resolved spectral analysis of the exceptional relic emission down to 6″ resolution over a broad range of frequencies. Our new sensitive radio images confirm the presence of complex filaments of magnetized relativistic plasma also at low frequencies. We find that the integrated spectrum of the relic is consistent with a single power law, without any sign of spectral steepening, at least below 3 GHz. Unlike previous claims, the relic shows an integrated spectral index of -1.07 ± 0.02 between 144 MHz and 3 GHz, which is consistent with the (quasi)stationary shock approximation. The spatially resolved spectral analysis suggests that the relic surface very likely traces the complex shock front, with a broad distribution of Mach numbers propagating through a turbulent and dynamically active intracluster medium. Our results show that the northern part of the relic is seen edge-on and the southern part close to face-on. We suggest that the complex filaments are regions where higher Mach numbers dominate the (re)acceleration of electrons that are responsible for the observed radio emission