SOUTHERN MASSIVE STARS AT HIGH ANGULAR RESOLUTION: OBSERVATIONAL CAMPAIGN AND COMPANION DETECTION (original) (raw)

HD?77407 and GJ?577: Two new young stellar binaries

Astronomy and Astrophysics, 2004

We present the first results from our search for close stellar and sub-stellar companions to young nearby stars on the northern sky. Our infrared imaging observations are obtained with the 3.5 m Calar Alto telescope and the AO system ALFA. With two epoch observations which were separated by about one year, we found two co-moving companion candidates, one close to HD 77407 and one close to GJ 577. For the companion candidate near GJ 577, we obtained an optical spectrum showing spectral type M 4.5; this candidate is a bound low-mass stellar companion confirmed by both proper motion and spectroscopy. We estimate the masses for HD 77407 B and GJ 577 B to be ∼0.3 to 0.5 M and ∼0.16 to 0.2 M , respectively. Compared to Siess et al. (2000) models, each of the two pairs appears co-eval with HD 77407 A, B being 10 to 40 Myrs and GJ 577 A, B being ≥100 Myrs old. We also took multi-epoch high-resolution spectra of HD 77407 to search for sub-stellar companions, but did not find any with 3 M Jup as upper mass (m sin i) limit (for up to 4 year orbits); however, we detected a long-term radial velocity trend in HD 77407 A, consistent with a ∼0.3 M companion at ∼50 AU separation, i.e. the one detected by the imaging. Hence, HD 77407 B is confirmed to be a bound companion to HD 77407 A. We also present limits for undetected, but detectable companions using a deep image of HD 77407 A and B, also observed with the Keck NIRC2 AO system; any brown dwarfs were detectable outside of 0.5 arcsec (17 AU at HD 77407), giant planets with masses from ∼6.5 to 12 M Jup were detectable at ≥1.5 arcsec.

A Survey of Stellar Families: Multiplicity of Solar-Type Stars

The Astrophysical Journal Supplement Series, 2010

We present the results of a comprehensive assessment of companions to solartype stars. A sample of 454 stars, including the Sun, was selected from the Hipparcos catalog with π > 40 mas, σ π /π < 0.05, 0.5 ≤ B − V ≤ 1.0 (∼ F6-K3), and constrained by absolute magnitude and color to exclude evolved stars. These criteria are equivalent to selecting all dwarf and subdwarf stars within 25 pc with V -band flux between 0.1 and 10 times that of the Sun, giving us a physical basis for the term "solar-type". New observational aspects of this work include surveys for (1) very close companions with long-baseline interferometry at the Center for High Angular Resolution Astronomy (CHARA) Array, (2) close companions with speckle interferometry, and (3) wide proper motion companions identified by blinking multi-epoch archival images. In addition, we include the results from extensive radial-velocity monitoring programs and evaluate companion information from various catalogs covering many different techniques. The results presented here include four new common proper motion companions discovered by blinking archival images. Additionally, the spectroscopic data searched reveal five new stellar companions. Our synthesis of results from many methods and sources results in a thorough evaluation of stellar and brown dwarf companions to nearby Sun-like stars.

A Spectroscopic Search for Colliding Stellar Winds in O‐Type Close Binary Systems. V. HD 149404

The Astrophysical Journal, 2001

We present new Ha emission-line spectra and an analysis of the mass outÑow for the massive close binary HD 149404. Spectra obtained between 1995 and 1997 show evidence of coherent orbital phaseÈ related variations superimposed on both long-term and short-term emission strength variations. We use a Doppler tomography algorithm to construct velocity maps of the emission intensity, and these demonstrate that emission displays two broad peaks that follow sinusoidal radial velocity curves that are sig-niÐcantly di †erent from the orbital velocity curves of either star. We present a model for the kinematics and distribution of the emitting circumstellar gas, and we argue that most of the emission comes from wind Ñows from both stars into a shock region between them. The binary appears to be in a postÈmass transfer stage in which systemic mass loss dominates the evolutionary processes.

Hot subdwarf stars in close-up view

Astronomy and Astrophysics, 2010

The origin of hot subdwarf B stars (sdBs) is still unclear. About half of the known sdBs are in close binary systems for which common envelope ejection is the most likely formation channel. Little is known about this dynamic phase of binary evolution. Since most of the known sdB systems are single-lined spectroscopic binaries, it is difficult to derive masses and unravel the companions' nature, which is the aim of this paper. Due to the tidal influence of the companion in close binary systems, the rotation of the primary becomes synchronised to its orbital motion. In this case it is possible to constrain the mass of the companion, if the primary mass, its projected rotational velocity as well as its surface gravity are known. For the first time we measured the projected rotational velocities of a large sdB binary sample from high resolution spectra. We analysed a sample of 51 sdB stars in close binaries, 40 of which have known orbital parameters comprising half of all such systems known today. Synchronisation in sdB binaries is discussed both from the theoretical and the observational point of view. The masses and the nature of the unseen companions could be constrained in 31 cases. We found orbital synchronisation most likely to be established in binaries with orbital periods shorter than 1.2 d. Only in five cases it was impossible to decide whether the sdB's companion is a white dwarf or an M dwarf. The companions to seven sdBs could be clearly identified as late M stars. One binary may have a brown dwarf companion. The unseen companions of nine sdBs are white dwarfs with typical masses. The mass of one white dwarf companion is very low. In eight cases (including the well known system KPD1930+2752) the companion mass exceeds 0.9 M , four of which even exceed the Chandrasekhar limit indicating that they may be neutron stars. Even stellar mass black holes are possible for the most massive companions. The distribution of the inclinations of the systems with low mass companions appears to be consistent with expectations, whereas a lack of high inclinations becomes obvious for the massive systems. We show that the formation of such systems can be explained with common envelope evolution and present an appropriate formation channel including two phases of unstable mass transfer and one supernova explosion. The sample also contains a candidate post-RGB star, which rotates fast despite its long orbital period. The post-RGB stars are expected to spin-up caused by their ongoing contraction. The age of the sdB is another important factor. If the EHB star is too young, the synchronisation process might not be finished yet. Estimating the ages of the target stars from their positions on the EHB band, we found PG 2345+318, which is known not to be synchronised, to lie near the zero-age extreme horizontal branch as are the massive candidates PG 1232−136, PG 1432+159 and PG 1101+249. These star may possibly be too young to have reached synchronisation. The derived large fraction of putative massive sdB binary systems in low inclination orbits is inconsistent with theoretical predictions. Even if we dismiss three candidates because they may be too young and assume that the other sdB primaries are of low mass, PG 1743+477 and, in particular, HE 0532−4503 remain as candidates whose companions may have masses close to or above the Chandrasekhar limit. X-ray observations and accurate photometry are suggested to clarify their nature. As high inclination systems must also exist, an appropriate survey has already been launched to find such binaries.

Characterization of very wide companion candidates to young stars with planets and disks

arXiv: Solar and Stellar Astrophysics, 2020

Discovering wide companions of stellar systems allows us to constrain the dynamical environment and age of the latter. We studied four probable wide companions of four different stellar systems. The central stars are V4046 Sgr, HIP 74865, HIP 65426, and HIP 73145, and their probable wide companions are 2MASS J18152222-3249329, 2MASS J15174874-3028484, 2MASS J13242119-5129503, and 2MASS J14571503-3543505 respectively. V4046 Sgr is a member of beta\betabeta-Pictoris Moving Group while the rest of the stellar systems are acknowledged as members of the Scorpius-Centaurus association. The selected stellar systems are particularly interesting because all of them are already known to possess a low-mass companion and/or a spatially resolved disk. Identifying wider companions of these stars can improve their eligibility as benchmarks for understanding the formation channels of various triple systems, and can help us to determine the orbits of their possibly undiscovered inner, wider companions in ...

«Multiwavelength study of the intriguing massive star CPD− 59 2629 (Tr 16-22)»

Bulletin de la Société …, 2011

We report preliminary results of a multi-wavelength (radio-optical-X-ray) study of the massive star CPD −59 2629 (Tr 16-22) in the Carina Nebula (NGC 3372). This star has historically shown a large X-ray excess (log L X /L bol < −6 or even larger), which is one order of magnitude larger than expected from single massive O-type stars. A colliding wind scenario is a plausible explanation. On this subject, we searched for non-thermal radio emission and used high-resolution optical spectroscopy to check for multiplicity and investigate the nature of the stars as well as the origin and excess of the X-ray emission. We detected long-term radial-velocity and X-ray variability. Both results suggest that Tr 16-22 is a long-term massive binary system and a variable colliding wind shock scenario.

The VLT/NaCo large program to probe the occurrence of exoplanets and brown dwarfs at wide orbits⋆

Context. Young, nearby stars are ideal targets to search for planets using the direct imaging technique. The determination of stellar parameters is crucial for the interpretation of imaging survey results, particularly since the luminosity of substellar objects has a strong dependence on system age. Aims. We have conducted a large program with NaCo at the VLT in order to search for planets and brown dwarfs in wide orbits around 86 stars. A large fraction of the targets observed with NaCo were poorly investigated in the literature. We performed a study to characterize the fundamental properties (age, distance, mass) of the stars in our sample. To improve target age determinations, we compiled and analyzed a complete set of age diagnostics. Methods. We measured spectroscopic parameters and age diagnostics using dedicated observations acquired with FEROS and CORALIE spectrographs at La Silla Observatory. We also made extensive use of archival spectroscopic data and results available in the literature. Additionally, we exploited photometric time-series, available in ASAS and Super-WASP archives, to derive rotation period for a large fraction of our program stars. Results. We provided updated characterization of all the targets observed in the VLT NaCo Large program, a survey designed to probe the occurrence of exoplanets and brown dwarfs in wide orbits. The median distance and age of our program stars are 64 pc and 100 Myr, respectively. Nearly all the stars have masses between 0.70 and 1.50 M⊙, with a median value of 1.01 M⊙. The typical metallicity is close to solar, with a dispersion that is smaller than that of samples usually observed in radial velocity surveys. Several stars are confirmed or proposed here to be members of nearby young moving groups. Eight spectroscopic binaries are identified.

Four new wide binaries among exoplanet host stars

Astronomy and Astrophysics, 2005

In our ongoing survey for wide (sub)stellar companions of exoplanet host stars we have found 4 new co-moving stellar companions of the stars HD 114729, HD 16141, HD 196050 and HD 213240 with projected separations from 223 up to 3898 AU. The companionship of HD 114729 B, HD 196050 B and HD 213240 C is confirmed by photometry and spectroscopy, all being early M dwarfs. The masses of the detected companions are derived from their infrared JHK magnitudes and range between 0.146 and 0.363 M ⊙ . Our first and second epoch observations can rule out additional stellar companions around the primaries from ∼ 200 up to ∼ 2400 AU (S/N=10).

Massive unseen companions to hot faint underluminous stars from SDSS (MUCHFUSS)

Astronomy & Astrophysics, 2011

The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims at finding hot subdwarf stars with massive compact companions like massive white dwarfs (M > 1.0 M), neutron stars or stellar mass black holes. The existence of such systems is predicted by binary evolution theory and recent discoveries indicate that they exist in our Galaxy. First results are presented for seven close binary sdBs with short orbital periods ranging from 0.21 d to 1.5 d. The atmospheric parameters of all objects are compatible with core helium-burning stars. The companions are most likely white dwarfs. In one case the companion could be shown to be a white dwarf by the absence of light-curve variations. However, in most cases late type main sequence stars cannot be firmly excluded. Comparing our small sample with the known population of close sdB binaries we show that our target selection method aiming at massive companions is efficient. The minimum companion masses of all binaries in our sample are high compared to the reference sample of known sdB binaries.