M-type Companion Research Articles

Discovery of an M-type companion to the Herbig Ae Star V1787 Ori

ABSTRACT The intermediate-mass Herbig Ae star V1787 Ori is a member of the L1641 star-forming region in the Orion A molecular cloud. We report the detection of an M-type companion to V1787 Ori at a projected separation of 6.66 arcsec (corresponding to 2577 au), from the analysis of VLT/NACO adaptive optics Ks-band image. Using astrometric data from Gaia DR2, we show that V1787 Ori A and B share similar distance (d ∼ 387 pc) and proper motion, indicating that they are physically associated. We estimate the spectral type of V1787 Ori B to be M5 ± 2 from colour–spectral type calibration tables and template matching using SpeX spectral library. By fitting PARSEC models in the Pan-STARRS colour–magnitude diagram, we find that V1787 Ori B has an age of 8.1$^{+1.7}_{-1.5}$ Myr and a mass of 0.39$^{+0.02}_{-0.05}$ M⊙. We show that V1787 Ori is a pre-main-sequence wide binary system with a mass ratio of 0.23. Such a low-mass ratio system is rarely identified in Herbig Ae/Be binary systems. We conclude this work with a discussion on possible mechanisms for the formation of V1787 Ori wide binary system.

THE NEW ECLIPSING CV MASTER OTJ192328.22+612413.5—A POSSIBLE SW SEXTANTIS STAR

ABSTRACT We present optical photometry and spectroscopy of the new eclipsing cataclysmic variable MASTER OTJ192328.22+612413.5, discovered by the MASTER team. We find the orbital period to be P = 0.16764612(5) day/4.023507(1) hr. The depth of the eclipse (2.9 ± 0.1 mag) suggests that the system is nearly edge on, and modeling of the system confirms the inclination to be between 81.°3 and 83.°6. The brightness outside the eclipse varies between observations, with a change of 1.6 ± 0.1 mag. Spectroscopy reveals double-peaked Balmer emission lines. By using spectral features matching a late M-type companion, we bound the distance to be 750 ± 250 pc, depending on the companion’s spectral type. The source displays 2 mag brightness changes on timescales of days. The amplitude of these changes, along with the spectrum at the faint state, suggest that the system is possibly a dwarf nova. The lack of any high-excitation He ii lines suggests that this system is not magnetically dominated. The light curve in both quiescence and outburst resembles that of Lanning 386, implying MASTER OTJ192328.22+612413.5 is a possible cross between a dwarf nova and a SW Sextantis star.

K2 DISCOVERY OF YOUNG ECLIPSING BINARIES IN UPPER SCORPIUS: DIRECT MASS AND RADIUS DETERMINATIONS FOR THE LOWEST MASS STARS AND INITIAL CHARACTERIZATION OF AN ECLIPSING BROWN DWARF BINARY

ABSTRACT We report the discovery of three low-mass double-lined eclipsing binaries in the pre-main sequence Upper Scorpius association, revealed by K2 photometric monitoring of the region over ∼78 days. The orbital periods of all three systems are <5 days. We use the K2 photometry plus multiple Keck/HIRES radial velocities (RVs) and spectroscopic flux ratios to determine fundamental stellar parameters for both the primary and secondary components of each system, along with the orbital parameters. We present tentative evidence that EPIC 203868608 is a hierarchical triple system comprised of an eclipsing pair of ∼25 M Jup brown dwarfs with a wide M-type companion. If confirmed, it would constitute only the second double-lined eclipsing brown dwarf binary system discovered to date. The double-lined system EPIC 203710387 is composed of nearly identical M4.5-M5 stars with fundamentally determined masses and radii measured to better than 3% precision ( M 1 = 0.1183 ± 0.0028 M ⊙ ?> , M 2 = 0.1076 ± 0.0031 M ⊙ ?> and R 1 = 0.417 ± 0.010 R ⊙ ?> , R 2 = 0.450 ± 0.012 R ⊙ ?> ) from combination of the light curve and RV time series. These stars have the lowest masses of any stellar mass double-lined eclipsing binary to date. Comparing our derived stellar parameters with evolutionary models, we suggest an age of ∼10–11 Myr for this system, in contrast to the canonical age of 3–5 Myr for the association. Finally, EPIC 203476597 is a compact single-lined system with a G8-K0 primary and a likely mid-K secondary whose lines are revealed in spectral ratios. Continued measurement of RVs and spectroscopic flux ratios will better constrain fundamental parameters and should elevate the objects to benchmark status. We also present revised parameters for the double-lined eclipsing binary UScoCTIO 5 ( M 1 = 0.3336 ± 0.0022 M ⊙ ?> , M 2 = 0.3200 ± 0.0022 M ⊙ ?> and R 1 = 0.862 ± 0.012 ?> , R 2 = 0.852 ± 0.013 R ⊙ ?> ), which are suggestive of a system age younger than previously reported. We discuss the implications of our results on these ∼0.1–1.5 M ⊙ ?> stars for pre-main-sequence evolutionary models.

YETI – search for young transiting planets

We present our search for young transiting planets at ages of 2 to 20 Myr. Towards this goal, we monitor a number of young open clusters with the YETI network. YETI consists of 0.4-2 m-sized telescopes at different longitudes that observe continuously over timescales much longer than a night. In our first cluster Trumpler 37 we found more than 350 variable stars. Also two transiting candidates were found so far, for which follow-up is partly done. The first candidate turned out to be an eclipsing binary with an M-type companion. We describe the research done on these two transiting candidates.

The unseen population of F- to K-type companions to hot subdwarf stars

We present a method to select hot subdwarf stars with A to M-type companions using photometric selection criteria. We cover a wide range in wavelength by combining GALEX ultraviolet data, optical photometry from the SDSS and the Carlsberg Meridian telescope, near-infrared data from 2MASS and UKIDSS. We construct two complimentary samples, one by matching GALEX, CMC and 2MASS, as well as a smaller, but deeper, sample using GALEX, SDSS and UKIDSS. In both cases, a large number of composite subdwarf plus main-sequence star candidates were found. We fit their spectral energy distributions with a composite model in order to estimate the subdwarf and companion star effective temperatures along with the distance to each system. The distribution of subdwarf effective temperature was found to primarily lie in the 20,000 - 30,000 K regime, but we also find cooler subdwarf candidates, making up ~5-10 per cent. The most prevalent companion spectral types were seen to be main-sequence stars between F0 and K0, while subdwarfs with M-type companions appear much rarer. This is clear observational confirmation that a very efficient first stable Roche-lobe overflow channel appears to produce a large number of subdwarfs with F to K-type companions. Our samples thus support the importance of binary evolution for subdwarf formation.

THE ALGOL SYSTEM SZ HERCULIS: PHYSICAL NATURE AND ORBITAL BEHAVIOR

Multiband CCD photometric observations of SZ Her were obtained between 2008 February and May. The light curve was completely covered and indicated a significant temperature difference between both components. The light-curve synthesis presented in this paper indicates that the eclipsing binary is a classical Algol-type system with parameters of $q$=0.472, $i$=87$^\circ$.57, and $\Delta$($T_{1}$--$T_{2}$)=2,381 K; the primary component fills approximately 77% of its limiting lobe and is slightly larger than the lobe-filling secondary. More than 1,100 times of minimum light spanning more than one century were used to study an orbital behavior of the binary system. It was found that the orbital period of SZ Her has varied due to a combination of two periodic variations with cycle lengths of $P_3$=85.8 yr and $P_4$=42.5 yr and semi-amplitudes of $K_3$=0.013 d and $K_4$=0.007 d, respectively. The most reasonable explanation for them is a pair of light-time effects (LITEs) driven by the possible existence of two M-type companions with minimum masses of $M_3$=0.22 M$_\odot$ and $M_4$=0.19 M$_\odot$, that are located close to the 2:1 mean motion resonance. If two additional bodies exist, then the overall dynamics of the multiple system may provide a significant clue to the formation and evolution of the eclipsing pair.

Period Changes of the Algol System SZ Herculis

AbstractNew CCD photometric observations of SZ Her were obtained between February and May 2008. More than 1,100 times of minimum light spanning more than one century were used for the period analysis. We find that the orbital period of SZ Her has varied due to a combination of two periodic variations, with cycle lengths of P3 = 85.8 yr and P4 = 42.5 yr and semi-amplitudes of K3 = 0.013 days and K4 = 0.007 days, respectively. The most reasonable explanation for them is a pair of light-time-travel (LTT) effects driven by the existence of two M-type companions with minimum masses of M3 = 0.22 M⊙ and M4 = 0.19 M⊙, located at nearly 2:1 mean motion resonance. Then, SZ Her is a quadruple system and the 3rd and 4th components would stay in the stable orbital resonance.

The New Eclipsing Cataclysmic Variable SDSS 154453+2553

ABSTRACTThe cataclysmic variable SDSS 154453 + 2553 was recently identified in the Sloan Digital Sky Survey. We obtained spectra and photometry at the MDM Observatory, which revealed an eclipse with a 6.03 hr period. The Hα emission line exhibits a strong rotational disturbance during eclipse, indicating that it arises in an accretion disk. A contribution from an M-type companion is also observed. Time-series photometry during eclipse gives an ephemeris of 2454878.0062(15) + 0.251282(2)E. We present spectroscopy through the orbit and eclipse photometry. Our analysis of the secondary star indicates a distance of 800 ± 180 pc.

An overtone Cepheid variable in an LMC eclipsing binary

AbstractEclipsing binary systems potentially allow the direct and precise determination of the important properties of their component stars. An eclipsing binary containing a Cepheid variable which is also a double-lined spectroscopic binary would allow, for the first time, the direct measurement of the absolute luminosity and mass of the Cepheid. The MACHO Project LMC database contains five systems whose light curves show variations due to both eclipses and pulsation but only one has been clearly identified as an intermediate-mass, Population I object. This object, MACHO 81.8997.87 (= OGLELMC_SC16 119952) is a 2.035-d overtone Cepheid in an 800.4-d binary system with an M-type companion. Here we present the results of the analysis of the light curve of this system, the implications for its evolutionary history and discuss the prospects for future observations.

A Protocometary Cloud around HR 4796A?

We report both ROSAT observations and ground-based 10.8 ?m imaging of the wide binary HR 4796, which consists of a main-sequence A-type star with a large amount of circumstellar dust, HR 4796A, and, at a separation of 77, a pre-main-sequence M-type companion, HR 4796B. From the ROSAT data, we find that the X-ray emission is centered on HR 4796B, with LX/Lbol ? 3 ? 10-4. The 10.8 ?m flux, which arises from HR 4796A, displays an excess over the photospheric emission of 0.08 ? 0.02 Jy, a result consistent with the previous characterization of the emission from the circumstellar dust in the wavelength range 12 ?m ? ? ? 100 ?m as a 110 K blackbody. The Hipparcos data can be used to argue that the three main-sequence A-type stars in the Bright Star Catalogue with LIR/Lbol > 10-3 (HR 4796A, ? Pic, and 49 Cet) all have low luminosities for their colors. We argue that approximately 20% of all A-type stars pass through an early phase where they possess an amount of circumstellar dust comparable to that found around HR 4796A or ? Pic. In order to explain the result that the grain emission can be approximated by a 110 K blackbody, we propose that the circumstellar grains are largely composed of ice particles with a typical radius near 100 ?m, and that they sublimate rapidly when they are closer than ~35 AU to HR 4796A. This swarm of ice particles might be a protocometary cloud.

Detection of an apparent star 2.1 arcsec from the circumstellar disk candidate Epsilon Sagittarii

view Abstract Citations (6) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detection of an apparent Star 2.1 Arcsec from the Circumstellar Disk Candidate Epsilon Sagittarii Golimowski, David A. ; Durrance, Samuel T. ; Clampin, Mark Abstract Optical images of the infrared excess star Epsilon Sagittarii obtained in 1990 and 1992 with the Adaptive Optics Coronagraph reveal a pointlike source, presumably a star, approximately 2.1 arcsec from Epsilon Sgr. Although the star appears partially occulted by the coronagraphic mask in the 1990 V- and R-band images, it is clearly resolved in the 1992 I-band image obtained with a smaller mask. Estimates of the V, R, and I magnitudes of the star are 7.7, 7.7, and 7.0, respectively. However, the large uncertainties in these estimates preclude an accurate assessment of the star's spectral type. Although the proximity of the star to Epsilon Sgr supports the hypothesis that previously reported optical and UV spectra of Epsilon Sgr are composite, the star appears too faint to account for the noted spectral anomalies. We speculate, however, that a K- or M-type companion to Epsilon Sgr may explain the observed infrared excess. Publication: The Astronomical Journal Pub Date: March 1993 DOI: 10.1086/116498 Bibcode: 1993AJ....105.1108G Keywords: Astronomical Photography; Infrared Stars; Stellar Envelopes; Astronomical Catalogs; Binary Stars; Companion Stars; Halos; Astronomy; CIRCUMSTELLAR MATTER; INFRARED: STARS; STARS: INDIVIDUAL: EPSILON SAGITTARII full text sources ADS | data products SIMBAD (2)