A possible surviving companion of the SN Ia in the Galactic SNR G272.2-3.2

We use the {\it Gaia} EDR3 to explore the Galactic supernova remnant SNR G272.2-3.2, produced by the explosion of a Type Ia supernova (SNIa), about 7,500 years ago, to search for a surviving companion. From the abundances in the SNR ejecta, G272.2-3.2 is a normal SN Ia. The {\it Gaia} parallaxes allow to select the stars located within the estimated distance range of the SNR, and the {\it Gaia} proper motions to study their kinematics. From the {\it Gaia} EDR3 photometry, we construct the HR diagram of the selected sample, which we compare with the theoretical predictions for the evolution of possible star companions of SNIa. We can discard several proposed types of companions by combining kinematics and photometry. We can also discard hypervelocity stars. We focus our study on the kinematically most peculiar star, {\it Gaia} EDR3 5323900215411075328 (hereafter MV-G272), a 8.9 $\sigma$ outlier in proper motion. It is of M1-M2 stellar type. Its trajectory on the sky locates it at the center of the SNR, 6,000--8,000 years ago, a unique characteristic among the the sample. Spectra allow a stellar parameters determination and a chemical abundance analysis. In conclusion, we have a candidate to be the surviving companion of the SN Ia that resulted in SNR G272.2-3.2. It is supported by its kinematical characteristics and its trajectory within the SNR. This opens the possibility of a single-degenerate scenario for a SN Ia with an M-type dwarf companion.Comment: 35 pages, 19 Figures, 5 Tables, published as ApJ 947, 90

Volatiles and refratories in solar analogs: No terrestial planet connection

We have analysed very high-quality HARPS and UVES spectra of 95 solar analogs, 24 hosting planets and 71 without detected planets, to search for any possible signature of terrestial planets in the chemical abundances of volatile and refractory elements with respect to the solar abundances. We demonstrate that stars with and without planets in this sample show similar mean abundance ratios, in particular, a sub-sample of 14 planet-host and 14 "single” solar analogs in the metallicity range 0.14 < [Fe/H] < 0.36. In addition, two of the planetary systems in this sub-sample, containing each of them a super-Earth-like planet with masses in the range ~ 7-11 Earth masses, have different volatile-to-refratory abundance ratios to what would be expected from the presence of a terrestial planets. Finally, we check that after removing the Galactic chemical evolution effects any possible difference in mean abundances, with respect to solar values, of refratory and volatile elements practically dissappear

Chemical clues on the formation of planetary systems

Theoretical studies suggest that C/O and Mg/Si are the most important elemental ratios in determining the mineralogy of terrestrial planets. The C/O ratio controls the distribution of Si among carbide and oxide species, while Mg/Si gives information about the silicate mineralogy. We find mineralogical ratios quite different from those of the Sun, showing that there is a wide variety of planetary systems which are not similar to Solar System. Many of planetary host stars present a Mg/Si value lower than 1, so their planets will have a high Si content to form species such as MgSiO3. This type of composition can have important implications for planetary processes like plate tectonics, atmospheric composition or volcanism. Moreover, the information given by these ratios can guide us in the search of stars more probable to form terrestrial planet

XTE J1118+480: A Metal-Rich Black Hole Binary in the Galactic Halo

We present medium-resolution optical spectra of the secondary star in the high Galactic latitude black hole X-ray binary XTE J1118+480 and determine the abundance of Mg, Al, Ca, Fe, and Ni in its atmosphere. For all the elements investigated we find supersolar abundances; thus, we reject the hypothesis that the black hole came from the direct collapse of an ancient massive halo star. The compact primary most likely formed in a supernova event of a massive star whose nucleosynthetic products polluted the secondary star. The observed element abundances and their ratios can be explained using a variety of supernova models with a wide range of metallicities. While an explosive origin in the Galactic halo or thick disk cannot be discarded, a metal-rich progenitor is clearly favored by the observed abundance pattern. This suggests that the black hole was produced in the Galactic thin disk with a violent natal kick, propelling the X-ray binary to its current location and orbit.Comment: Accepted for publication as a letter in The Astrophysical Journa

The Chemical Abundances of Tycho G in Supernova Remnant 1572

We present an analysis of the chemical abundances of the star Tycho G in the direction of the remnant of supernova (SN) 1572, based on Keck high-resolution optical spectra. The stellar parameters of this star are found to be those of a G-type subgiant with $T_{\mathrm{eff}} = 5900 \pm 100$ K, \loggl $= 3.85 \pm 0.30$ dex, and $\mathrm{[Fe/H]} = -0.05 \pm 0.09$. This determination agrees with the stellar parameters derived for the star in a previous survey for the possible companion star of SN 1572 (Ruiz-Lapuente et al. 2004). The chemical abundances follow the Galactic trends, except for Ni, which is overabundant relative to Fe, $[{\rm Ni/Fe}]$ $=$ 0.16 $\pm$ 0.04. Co is slightly overabundant (at a low significance level). These enhancements in Fe-peak elements could have originated from pollution by the supernova ejecta. We find a surprisingly high Li abundance for a star that has evolved away from the main sequence. We discuss these findings in the context of companion stars of supernovae.Comment: Accepted for publication in the Astrophysical Journa