Multiplicity Study of Exoplanet Host Stars

We present recent results of our ongoing multiplicity study of exoplanet host stars.Comment: 3 pages, 3 figure

Gaia search for stellar companions of TESS objects of interest II

We present the latest results of our ongoing multiplicity study of (Community) TESS Objects of Interest, using astro‐ and photometric data from the ESA‐Gaia mission, to detect stellar companions of these stars and to characterize their properties. In total, 107 binary, 5 hierarchical triple star systems, as well as one quadruple system were detected among 585 targets surveyed, which are all located at distances closer than about 500 pc around the Sun. As proven with their accurate Gaia EDR3 astrometry, the companions and the targets are located at the same distance and share a common proper motion, as it is expected for components of gravitationally bound stellar systems. The companions exhibit masses in the range between about 0.09 M ⊙ and 4.5 M ⊙ and are most frequently found in the mass range between 0.15 and 0.6 M ⊙ . The companions are separated from the targets by about 120 up to 9,500 au and their frequency is the highest and constant within about 500 au while it continually decreases for larger separations. Beside mainly early to mid M dwarfs, also five white dwarf companions were identified in this survey, whose true nature was revealed by their photometric properties

Gaia search for stellar companions of TESS Objects of Interest III

The latest results from our ongoing multiplicity study of (Community) TESS Objects of Interest are presented, using astro‐ and photometric data from the ESA‐Gaia mission, to detect stellar companions of these stars and characterize their properties. A total of 124 binary and 7 hierarchical triple star systems were detected among 2175 targets, whose multiplicity was investigated in the course of our survey, which are located at distances closer than about 500 pc around the Sun. The detected companions and the targets are located at the same distance and share a common proper motion, as expected for components of gravitationally bound stellar systems, as proven with their accurate Gaia EDR3 astrometry. The companions have masses in the range between about 0.09 and 2.5 M ⊙ $${M}_{\odot }$$ and are most frequently found in the mass range between 0.15 and 0.8 M ⊙ $${M}_{\odot }$$ . The companions exhibit projected separations to the targets between about 50 to 9700 au and their frequency is the highest and constant up to about 500 au, while it decreases for larger projected separations. In addition to mainly mid M to early K dwarfs, 4 white dwarf companions were also detected in this survey, whose true nature could be identified with their photometric properties

Discovery of an OB Runaway Star Inside SNR S147

We present first results of a long term study: Searching for OB--type runaway stars inside supernova remnants (SNRs). We identified spectral types and measured radial velocities (RV) by optical spectroscopic observations and we found an early type runaway star inside SNR S147. HD 37424 is a B0.5V type star with a peculiar velocity of 74$\pm$8 km s$^{-1}$. Tracing back the past trajectories via Monte Carlo simulations, we found that HD 37424 was located at the same position as the central compact object, PSR J0538+2817, $30\!\pm\!4$ kyr ago. This position is only $\sim$4 arcmin away from the geometrical center of the SNR. So, we suggest that HD 37424 was the pre--supernova binary companion to the progenitor of the pulsar and the SNR. We found a distance of 1333$^{+103}_{-112}$ pc to the SNR. The zero age main sequence progenitor mass should be greater than 13 $M_\odot$. The age is $30\pm4$ kyr and the total visual absorption towards the center is 1.28$\pm$0.06 mag. For different progenitor masses, we calculated the pre--supernova binary parameters. The Roche Lobe radii suggest that it was an interacting binary in the late stages of the progenitor.Comment: Accepted to be published in MNRAS, 10 pages, 5 figure

How many suns are in the sky? A SPHERE multiplicity survey of exoplanet host stars I -- Four new close stellar companions including a white dwarf

We are studying the influence of stellar multiplicity on exoplanet systems, in particular systems that have been detected via radial-velocity searches. We are in particular interested in the closest companions as they would have a strong influence on the evolution of the original planet forming disks. In this study we present new companions detected during our ongoing survey of exoplanet hosts with VLT/SPHERE. We are using the extreme adaptive optics imager SPHERE at the ESO/VLT to search for faint (sub)stellar companions. We utilized the classical coronagraphic imaging mode to perform a snapshot survey (3-6 min integration time) of exoplanet host stars in the Ks-band. We detected new stellar companions to the exoplanet host stars HD1666, HIP68468, HIP107773, and HD109271. With an angular separation of only 0.38" (40 au of projected separation) HIP107773 is among the closest companions found to exoplanet host stars. The presence of the stellar companion explains the linear radial-velocity trend seen in the system. At such a small separation the companion likely had significant influence on the evolution of the planet forming disk around the primary star. We find that the companion in the HD1666 system may well be responsible for the high orbit eccentricity (0.63) of the detected Jupiter class planet, making this system one of only a few where such a connection can be established. A cross-match with the Gaia DR2 catalog showed furthermore that the near infrared faint companion around HD109271 had been detected in the optical and is significantly brighter than in the near infrared making it a white dwarf companion.Comment: 8 pages, 4 figures, accepted for publication by A&

Identification of additional young nearby runaway stars based on Gaia data release 2 observations and the lithium test

Runaway stars are characterized by their remarkably high space velocities, and the study of their formation mechanisms has attracted considerable interest. Young, nearby runaway stars are the most favorable for identifying their place of origin, and for searching for possible associated objects such as neutron stars. Usually, the research field of runaway stars focuses on O‐ and B‐type stars, because these objects are better detectable at larger distances than late‐type stars. Early‐type runaway stars have the advantage that they evolve faster and can therefore better be confirmed to be young. In contrast to this, the catalog of Young runaway stars within 3 kpc by Tetzlaff, N., Neuhäuser, R., & Hohle, M. M. (2011, MNRAS, 410(1), 190–200) contains also stars of spectral type A and later. The objects in this catalog were originally classified as young ( ≤ 50 Myr) runaway stars by using Hipparcos data to estimate the ages from their location in the Hertzsprung‐Russell diagram and evolutionary models. In this article, we redetermine and/or constrain their ages not only by using the more precise second data release of the Gaia mission, but also by measuring the equivalent width of the lithium (6,708 Å) line, which is a youth indicator. Therefore, we searched for lithium absorption in the spectra of 51 target stars, taken at the University Observatory Jena between March and September 2020 with the Échelle spectrograph FLECHAS, and within additional TRES‐spectra from the Fred L. Whipple Observatory. The main part of this campaign with its 308 reduced spectra, accessible at VizieR , was already published. In this work, which is the continuation and completion of the in 2015 initiated observing campaign, we found three additional young runaway star candidates

Toward Understanding the Origin of Turbulence in Molecular Clouds: Small Scale Structures as Units of Dynamical Multi-Phase Interstellar Medium

In order to investigate the origin of the interstellar turbulence, detailed observations in the CO J=1--0 and 3--2 lines have been carried out in an interacting region of a molecular cloud with an HII region. As a result, several 1,000 to 10,000 AU scale cloudlets with small velocity dispersion are detected, whose systemic velocities have a relatively large scatter of a few km/s. It is suggested that the cloud is composed of small-scale dense and cold structures and their overlapping effect makes it appear to be a turbulent entity as a whole. This picture strongly supports the two-phase model of turbulent medium driven by thermal instability proposed previously. On the surface of the present cloud, the turbulence is likely to be driven by thermal instability following ionization shock compression and UV irradiation. Those small scale structures with line width of ~ 0.6 km/s have a relatively high CO line ratio of J=3--2 to 1--0, 1 < R(3-2/1-0) < 2. The large velocity gradient analysis implies that the 0.6 km/s width component cloudlets have an average density of 10^{3-4} cm^{-3}, which is relatively high at cloud edges, but their masses are only < 0.05 M_{sun}.Comment: 12 pages, 9 figures. To be published in the Astrophysical Journa