On the Biohabitability of M-dwarf Planets

Abstract

The recent detection of Earth-sized planets in the habitable zone of Proxima Centauri, Trappist-1 and many other nearby M-type stars has led to speculations, whether liquid water and life actually exist on these planets. To a large extent, the answer depends on their yet unknown atmospheres, which may though be within observational reach in the near future by JWST, ELT and other planned telescopes. We consider the habitability of planets of M-type stars in the context of their atmospheric properties, heat transport and irradiation. Instead of the traditional definition of the habitable zone, we define the bio-habitable zone, where liquid water and complex organic molecules can survive on at least part of the planetary surface. The atmospheric impact on the temperature is quantified in terms of the heating factor (a combination of greenhouse heating, stellar irradiation, albedo etc.) and heat redistribution (horizontal energy transport). We investigate the bio-habitable domain (where planets can support surface liquid water and organics) in terms of these two factors. Our results suggest that planets orbiting M-type stars may have life-supporting temperatures, at least on part of their surface, for a wide range of atmospheric properties. We apply this analyses to Proxima b and the Trappist-1 system. Finally we discuss the implications to the search of biosignatures and demonstrate how they may be used to estimate the abundance of photosynthesis and biotic planets.

LLAMA: TheMBH–σ⋆relation of the most luminous local AGNs

“…They are in the range of 6.34 ≤ log M BH ≤ 7.75 M for Hα. We note that the average black hole mass of inactive galaxies in the relation by Kormendy & Ho (2013) is substantially higher, possibly indicating that our sample of AGNs did not yet go through a major merger phase (Wandel et al 1999).…”

The Radius–Luminosity Relationship Depends on Optical Spectra in Active Galactic Nuclei

“…In combination with the velocity width (∆V ) of the emission line, RM measurement yields an estimate of BH mass as (e.g., Wandel et al 1999;Peterson et al 2004), where G is the gravitational constant, and f BLR is the virial factor related to the geometry and kinematics of the BLR (e.g., Onken et al 2004;Park et al 2012;Grier et al 2013a;Ho & Kim 2014;Woo et al 2015). Although measuring BH mass through RM technique is feasible for a small number of objects, it is not easy to apply RM to large AGN samples because RM is fairly time-consuming (always continuing for months to years).…”

Active Galactic Nuclei with Ultrafast Outflows Monitoring Project: The Broad-line Region of Mrk 79 as a Disk Wind

“…BH masses of ∼100 AGNs have been measured by different RM campaigns (e.g., Peterson et al 1993bPeterson et al , 1998Kaspi et al 2000;Peterson et al 2004;Denney et al 2009bDenney et al , 2010Bentz et al 2007Bentz et al , 2009bBentz et al , 2010Bentz et al , 2013Barth et al 2011a,b;Peterson 2014;Du et al 2015;Grier et al 2017;Du et al 2018;De Rosa et al 2018). Canonical Radius−Luminosity relationship is constructed from these RM campaigns (Peterson et al 1993b;Wandel et al 1999;Kaspi et al 2000;Bentz et al 2013), which provides an indirect way to estimate BH mass from single spectrum. However, as the number of sample increases, this relationship becomes more scatter (∼0.3 dex; Bentz et al 2013;Grier et al 2017;Du et al 2018).…”