Primeval very low-mass stars and brown dwarfs - VII. The discovery of the first wide M + L extreme subdwarf binary
Abstract
I present the discovery of the first wide M + L extreme subdwarf binary system Gaia J0452-36AB. The binary is located at a distance of 137.27 ^{+0.68}_{-0.67} pc with a projected separation of 15828 ± 78 au. I classified Gaia J0452-36AB as esdM1 and esdL0 subdwarfs, respectively. Gaia J0452-36AB have typical halo kinematics, metallicity of [Fe/H] ≈-1.4, and temperature of ∼ 3550 and 2600 K, respectively. Gaia J0452-36AB is a pair of very low-mass stars with masses of 0.151 ^{+0.029}_{-0.019} and 0.0855^{+0.0014}_{-0.0010} M\odot, and is a gravitationally bound system. I tested the metallicity consistency of existing M subdwarf classification schemes with Gaia J0452-36AB and a sample of M and L subdwarfs with known metallicity. I found that the metallicity of each M subclass defined by the the metallicity index ζCaH/TiO is not consistent from mid-to-late M subtypes. Because late-type M and L subdwarfs have dusty atmospheres and high surface gravity which have significant impacts on CaH and TiO indices that used in the classification. The metallicity scale of late-type M subdwarfs would be overestimated by the ζCaH/TiO index. I discussed the mass range of M subdwarfs, and explained the lack of late-type M extreme and ultra subdwarfs, and decreasing binary fraction from sdM, to esdM, and usdM subclasses. The four M subclasses have different mass ranges. The comparison between M subclasses is between populations in different mass ranges. I also present the discovery of Ruiz 440-469B, an M8 dwarf wide companion to a cool DA white dwarf, Ruiz 440-469.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- October 2019
- DOI:
- 10.1093/mnras/stz2196
- arXiv:
- arXiv:1908.02390
- Bibcode:
- 2019MNRAS.489.1423Z
- Keywords:
-
- binaries: general;
- brown dwarfs;
- stars: individual: Gaia J045238.82-361001.3;
- Gaia J045245.87-360843.8;
- Gaia J115626.32-322227.1;
- stars: low-mass;
- stars: Population II;
- subdwarfs;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 14 pages, 10 figures