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Register a new userNU Ori: a hierarchical triple system with a strongly magnetic B-type star
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NU Ori is a massive spectroscopic and visual binary in the Orion Nebula Cluster, with 4 components: Aa, Ab, B, and C. The B0.5 primary (Aa) is one of the most massive B-type stars reported to host a magnetic field. We report the detection of a spectroscopic contribution from the C component in high-resolution ESPaDOnS spectra, which is also detected in a Very Large Telescope Interferometer (VLTI) dataset. Radial velocity (RV) measurements of the inner binary (designated Aab) yield an orbital period of 14.3027(7) d. The orbit of the third component (designated C) was constrained using both RVs and interferometry. We find C to be on a mildly eccentric 476(1) d orbit. Thanks to spectral disentangling of mean line profiles obtained via least-squares deconvolution we show that the Zeeman Stokes $V$ signature is clearly associated with C, rather than Aa as previously assumed. The physical parameters of the stars were constrained using both orbital and evolutionary models, yielding $M_{rm Aa} = 14.9 pm 0.5 M_odot$, $M_{rm Ab} = 3.9 pm 0.7 M_odot$, and $M_{rm C} = 7.8 pm 0.7 M_odot$. The rotational period obtained from longitudinal magnetic field $langle B_z rangle$ measurements is $P_{rm rot} = 1.09468(7)$ d, consistent with previous results. Modeling of $langle B_z rangle$ indicates a surface dipole magnetic field strength of $sim 8$ kG. NU Ori C has a magnetic field strength, rotational velocity, and luminosity similar to many other stars exhibiting magnetospheric H$alpha$ emission, and we find marginal evidence of emission at the expected level ($sim$1% of the continuum).
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We present our analysis of HD~35502 based on high- and medium-resolution spectropolarimetric observations. Our results indicate that the magnetic B5IVsnp star is the primary component of a spectroscopic triple system and that it has an effective temperature of $18.4pm0.6,{rm kK}$, a mass of $5.7pm0.6,M_odot$, and a polar radius of $3.0^{+1.1}_{-0.5},R_odot$. The two secondary components are found to be essentially identical A-type stars for which we derive effective temperatures ($8.9pm0.3,{rm kK}$), masses ($2.1pm0.2,M_odot$), and radii ($2.1pm0.4,R_odot$). We infer a hierarchical orbital configuration for the system in which the secondary components form a tight binary with an orbital period of $5.66866(6),{rm d}$ that orbits the primary component with a period of over $40,{rm yrs}$. Least-Squares Deconvolution (LSD) profiles reveal Zeeman signatures in Stokes $V$ indicative of a longitudinal magnetic field produced by the B star ranging from approximately $-4$ to $0,{rm kG}$ with a median uncertainty of $0.4,{rm kG}$. These measurements, along with the line variability produced by strong emission in H$alpha$, are used to derive a rotational period of $0.853807(3),{rm d}$. We find that the measured $vsin{i}=75pm5,{rm km,s}^{-1}$ of the B star then implies an inclination angle of the stars rotation axis to the line of sight of $24^{+6}_{-10}degree$. Assuming the Oblique Rotator Model, we derive the magnetic field strength of the B stars dipolar component ($14^{+9}_{-3},{rm kG}$) and its obliquity ($63pm13degree$). Furthermore, we demonstrate that the calculated Alfv{e}n radius ($41^{+17}_{-6},R_ast$) and Kepler radius ($2.1^{+0.4}_{-0.7},R_ast$) place HD~35502s central B star well within the regime of centrifugal magnetosphere-hosting stars.
Time series of spectroscopic, speckle-interferometric, and optical long-baseline-interferometric observations confirm that $ u$ Gem is a hierarchical triple system. It consists of an inner binary composed of two B-type stars and an outer classical Be star. Several photospheric spectral lines of the inner components were disentangled, revealing two stars with very different rotational broadening ($sim$260 and $sim$140 kms$^{-1}$, respectively), while the photospheric lines of the Be star remain undetected. From the combined spectroscopic and astrometric orbital solution it is not possible to unambiguously cross-identify the inner astrometric components with the spectroscopic components. In the preferred solution based on modeling of the disentangled line profiles, the inner binary is composed of two stars with nearly identical masses of 3.3 M$_odot$ and the more rapidly rotating star is the fainter one. These two stars are in a marginally elliptical orbit ($e$ = 0.06) about each other with a period of 53.8 d. The third star also has a mass of 3.3 M$_odot$ and follows a more eccentric ($e$ = 0.24) orbit with a period of 19.1 yr. The two orbits are co-directional and, at inclinations of 79$^{circ}$ and 76$^{circ}$ of the inner and the outer orbit, respectively, about coplanar. No astrometric or spectroscopic evidence could be found that the Be star itself is double. The system appears dynamically stable and not subject to eccentric Lidov-Kozai oscillations. After disentangling, the spectra of the components of the inner binary do not exhibit peculiarities that would be indicative of past interactions. Motivations for a wide range of follow-up studies are suggested.
GW Ori is a hierarchical triple system which has a rare circumtriple disk. We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of 1.3 mm dust continuum and 12CO J=2-1 molecular gas emission of the disk. For the first time, we identify three dust rings in the disk at ~46, 188, and 338 AU, with estimated dust mass of ~70-250 Earth masses, respectively. To our knowledge, the outer ring in GW Ori is the largest dust ring ever found in protoplanetary disks. We use visibility modelling of dust continuum to show that the disk has misaligned parts and the innermost dust ring is eccentric. The disk misalignment is also suggested by the CO kinematics modelling. We interpret these substructures as evidence of ongoing dynamical interactions between the triple stars and the circumtriple disk.
We report the detection of a wide young hierarchical triple system where the primary has a candidate debris disc. The primary, TYC 5241-986-1 A, is a known Tycho star which we classify as a late-K star with emission in the X-ray, near and far-UV and Halpha suggestive of youth. Its proper motion, photometric distance (65-105 pc) and radial velocity lead us to associate the system with the broadly defined Local Association of young stars but not specifically with any young moving group. The presence of weak lithium absorption and X-ray and calcium H and K emission support an age in the 20 to ~125 Myr range. The secondary is a pair of M4.5+-0.5 dwarfs with near and far UV and Halpha emission separated by approximately 1 arcsec (~65-105 AU projected separation) which lie 145 arcsec (9200-15200 AU) from the primary. The primary has a WISE 22 micron excess and follow-up Herschel observations also detect an excess at 70 micron. The excess emissions are indicative of a 100-175 K debris disc. We also explore the possibility that this excess could be due to a coincident background galaxy and conclude that this is unlikely. Debris discs are extremely rare around stars older than 15 Myr, hence if the excess is caused by a disc this is an extremely novel system.
Ground-based optical long-baseline interferometry has the power to measure the orbits of close binary systems at ~10 micro-arcsecond precision. This precision makes it possible to detect wobbles in the binary motion due to the gravitational pull from additional short period companions. We started the ARrangement for Micro-Arcsecond Differential Astrometry (ARMADA) survey with the MIRC-X instrument at the CHARA array for the purpose of detecting giant planets and stellar companions orbiting individual stars in binary systems. We describe our observations for the survey, and introduce the wavelength calibration scheme that delivers precision at the tens of micro-arcseconds level for <0.2 arcsecond binaries. We test our instrument performance on a known triple system kappa Peg, and show that our survey is delivering a factor of 10 better precision than previous similar surveys. We present astrometric detections of tertiary components to two B-type binaries: a 30-day companion to alpha Del, and a 50-day companion to nu Gem. We also collected radial velocity data for alpha Del with the Tennessee State University Automated Spectroscopic Telescope at Fairborn Observatory. We are able to measure the orbits and masses of all three components in these systems. We find that the previously published RV orbit for the inner pair of nu Gem is not consistent with our visual orbit. The precision achieved for these orbits suggests that our ARMADA survey will be successful at discovering new compact triple systems to A/B-type binary systems, leading to better statistics of hierarchical system architectures and formation history.
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