We derive the distance and structure of the Perseus molecular cloud by combining trigonometric parallaxes from Very Long Baseline Array (VLBA) observations, taken as part of the GOBELINS survey and ...Gaia Data Release 2. Based on our VLBA astrometry, we obtain a distance of 321 10 pc for IC 348. This is fully consistent with the mean distance of 320 26 measured by Gaia. The VLBA observations toward NGC 1333 are insufficient to claim a successful distance measurement to this cluster. Gaia parallaxes, on the other hand, yield a mean distance of 293 22 pc. Hence, the distance along the line of sight between the eastern and western edges of the cloud is ∼30 pc, which is significantly smaller than previously inferred. We use Gaia proper motions and published radial velocities to derive the spatial velocities of a selected sample of stars. The average velocity vectors with respect to the LSR are = (−6.1 1.6, 6.8 1.1, −0.9 1.2) and (−6.4 1.0, 2.1 1.4, −2.4 1.0) km s−1 for IC 348 and NGC 1333, respectively. Finally, our analysis of the kinematics of the stars has shown that there is no clear evidence of expansion, contraction, or rotational motions within the clusters.
A VLBI resolution of the Pleiades distance controversy Melis, Carl; Reid, Mark J.; Mioduszewski, Amy J. ...
Science (American Association for the Advancement of Science),
08/2014, Letnik:
345, Številka:
6200
Journal Article
Recenzirano
Odprti dostop
Because of its proximity and its youth, the Pleiades open cluster of stars has been extensively studied and serves as a cornerstone for our understanding of the physical properties of young stars. ...This role is called into question by the “Pleiades distance controversy,” wherein the cluster distance of 120.2 ± 1.5 parsecs (pc) as measured by the optical space astrometry mission Hipparcos is significantly different from the distance of 133.5 ± 1.2 pc derived with other techniques. We present an absolute trigonometric parallax distance measurement to the Pleiades cluster that uses very long baseline radio interferometry (VLBI). This distance of 136.2 ± 1.2 pc is the most accurate and precise yet presented for the cluster and is incompatible with the Hipparcos distance determination. Our results cement existing astrophysical models for Pleiades-age stars.
We present Gaia-DR2 astrometry of a sample of YSO candidates in Ophiuchus, Serpens Main, and Serpens South/W40 in the Aquila Rift, which had been mainly identified by their infrared excess with ...Spitzer. We compare the Gaia-DR2 parallaxes against published and new parallaxes obtained from our Very Long Baseline Array (VLBA) program Gould's Belt Distances Survey. We obtain consistent results between Gaia and the VLBA for the mean parallaxes in each of the regions analyzed here. We see small offsets, when comparing mean values, of a few tens of microarcseconds in the parallaxes, which are either introduced by the Gaia zero-point error or due to a selection effect by Gaia toward the brightest, less obscured stars. Gaia-DR2 data alone conclusively places Serpens Main and Serpens South at the same distance, as we first inferred from VLBA data alone in a previous publication. Thus, Serpens Main, Serpens South, and W40 are all part of the same complex of molecular clouds, located at a mean distance of 436 9 pc. In Ophiuchus, both Gaia and VLBA suggest a small parallax gradient across the cloud, and the distance changes from 144.2 1.3 to 138.4 2.6 pc when going from L1689 to L1688.
We present new trigonometric parallaxes and proper motions of young stellar objects in the Taurus molecular cloud complex from observations collected with the Very Long Baseline Array as part of the ...Gould's Belt Distances Survey. We detected 26 young stellar objects and derived trigonometric parallaxes for 18 stars with an accuracy of 0.3% to a few percent. We modeled the orbits of six binaries and determined the dynamical masses of the individual components in four of these systems (V1023 Tau, T Tau S, V807 Tau, and V1000 Tau). Our results are consistent with the first trigonometric parallaxes delivered by the Gaia satellite and reveal the existence of significant depth effects. We find that the central portion of the dark cloud Lynds 1495 is located at d =129.5 0.3 pc, while the B216 clump in the filamentary structure connected to it is at d = 158.1 1.2 pc. The closest and remotest stars in our sample are located at d = 126.6 1.7 pc and d = 162.7 0.8 pc, yielding a distance difference of about 36 pc. We also provide a new distance estimate for HL Tau that was recently imaged. Finally, we compute the spatial velocity of the stars with published radial velocity and investigate the kinematic properties of the various clouds and gas structures in this region.
ABSTRACT We present the first results of the Gould's Belt Distances Survey (GOBELINS), a project aimed at measuring the proper motion and trigonometric parallax of a large sample of young stars in ...nearby regions using multi-epoch Very Long Baseline Array (VLBA) radio observations. Enough VLBA detections have now been obtained for 16 stellar systems in Ophiuchus to derive their parallax and proper motion. This leads to distance determinations for individual stars with an accuracy of 0.3 to a few percent. In addition, the orbits of six multiple systems were modelled by combining absolute positions with VLBA (and, in some cases, near-infrared) angular separations. Twelve stellar systems are located in the dark cloud Lynds 1688; the individual distances for this sample are highly consistent with one another and yield a mean parallax for Lynds 1688 of mas, corresponding to a distance pc. This represents an accuracy greater than 1%. Three systems for which astrometric elements could be measured are located in the eastern streamer (Lynds 1689) and yield an estimate of mas, corresponding to a distance pc. This suggests that the eastern streamer is located about 10 pc farther than the core, but this conclusion needs to be confirmed by observations of additional sources in the eastern streamer (currently being collected). From the measured proper motions, we estimate the one-dimensional velocity dispersion in Lynds 1688 to be 2.8 1.8 and 3.0 2.0 km s−1, in R.A. and decl., respectively; these are larger than, but still consistent within of, those found in other studies.
Astrometric observations of the M9 dwarf TVLM 513-46546 taken with the VLBA reveal an astrometric signature consistent with a period of 221 5 days. The orbital fit implies that the companion has a ...mass mp = 0.35−0.42 MJ, a circular orbit (e 0), a semimajor axis a = 0.28−0.31 au, and an inclination angle i = 71°−88°. The detected companion, TVLM 513b, is one of the few giant-mass planets found associated with ultracool dwarfs. The presence of a Saturn-like planet on a circular orbit 0.3 au from a 0.06−0.08 M star represents a challenge to planet formation theory. This is the first astrometric detection of a planet at radio wavelengths.
Abstract LP 349−25 is a well-studied close stellar binary system comprised of two late M dwarf stars, where both stars are close to the limit between star and brown dwarf. This system was previously ...identified as a source of gigahertz radio emission. We observed LP 349−25AB over 11 epochs in 2020–2022, detecting both components in this nearby binary system using the Very Long Baseline Array (VLBA). We fit simultaneously the VLBA absolute astrometric positions together with existing relative astrometric observations derived from optical/infrared observations with a set of algorithms that use nonlinear least-squares, genetic algorithm, and Markov Chain Monte Carlo methods to determine the orbital parameters of the two components. We find the masses of the primary and secondary components to be 0.08188 ± 0.00061 M ⊙ and 0.06411 ± 0.00049 M ⊙ , respectively, representing one of the most precise mass estimates of any ultracool dwarf (UCD) to date. The primary is a UCD of 85.71 ± 0.64 M Jup , while the secondary has a mass consistent with being a brown dwarf of 67.11 ± 0.51 M Jup . This is one of the very few direct detections of a brown dwarf with VLBA observations. We also find a distance to the binary system of 14.122 ± 0.057 pc. Using stellar evolutionary models, we find the model-derived stellar parameters of both stars. In particular, we obtain a model-derived age of 262 Myr for the system, which indicates that LP 349−25AB is composed of two pre–main-sequence stars. In addition, we find that the secondary star is significantly less evolved than the primary star.
ABSTRACT We present the results of the Gould's Belt Distances Survey of young star-forming regions toward the Orion Molecular Cloud Complex. We detected 36 young stellar objects (YSOs) with the Very ...Large Baseline Array, 27 of which have been observed in at least three epochs over the course of two years. At least half of these YSOs belong to multiple systems. We obtained parallax and proper motions toward these stars to study the structure and kinematics of the Complex. We measured a distance of 388 5 pc toward the Orion Nebula Cluster, 428 10 pc toward the southern portion L1641, 388 10 pc toward NGC 2068, and roughly ∼420 pc toward NGC 2024. Finally, we observed a strong degree of plasma radio scattering toward λ Ori.
Abstract
We report on the X-ray spectral and spatial evolution of the symbiotic star R Aqr. Through a multiepoch observational campaign performed with Chandra between 2017 and 2022, we study the ...X-ray emission of this binary system, composed of an evolved red giant star and a white dwarf (WD). This analysis is particularly timely as the WD approached the periastron in late 2018/early 2019; thus, mass transfer, jet emission, and outburst phenomena are to be expected. Through detailed spectral analysis, we detect a significant rise in the soft X-ray (0.5–2 keV) emission of R Aqr, likely linked to jet emission, followed by a decay toward the previous quiescent state. The hard X-ray emission (5–8 keV) is not immediately affected by the periastron passage; the hard component, after maintaining the same flux level between 2017 and 2021, rapidly decays after 2022. Possible explanations for this are a change in the reflection properties of the medium surrounding the binary, obscuration of the central region by material ejected during the periastron passage, or even the partial/complete destruction of the inner regions of the accretion disk surrounding the WD. In addition to this activity in the central region, extended emission is also detected, likely linked to a hot spot in a pre-outburst-emitted jet, which can be observed moving away from the system’s central region.
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