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تسجيل مستخدم جديدThe Goulds Belt distance survey
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تأليف
L. Loinard
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Very Long Baseline Interferometry (VLBI) observations can provide the position of compact radio sources with an accuracy of order 50 micro-arcseconds. This is sufficient to measure the trigonometric parallax and proper motions of any object within 500 pc of the Sun to better than a few percent. Because they are magnetically active, young stars are often associated with compact radio emission detectable using VLBI techniques. Here we will show how VLBI observations have already constrained the distance to the most often studied nearby regions of star-formation (Taurus, Ophiuchus, Orion, etc.) and have started to provide information on their internal structure and kinematics. We will then briefly describe a large project (called The Goulds Belt Distance Survey) designed to provide a detailed view of star-formation in the Solar neighborhood using VLBI observations.
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Very Long Baseline Interferometry (VLBI) observations can provide the position of compact radio sources with an accuracy of order 50 micro-arcseconds. This is sufficient to measure the trigonometric parallax and proper motions of any object within 50
0 pc of the Sun to better than a few percent. Because they are magnetically active, young stars are often associated with compact radio emission detectable using VLBI techniques. Here we will show how VLBI observations have already constrained the distance to the most often studied nearby regions of star-formation (Taurus, Ophiuchus, Orion, etc.) and have started to provide information on their internal structure and kinematics. We will then briefly describe a large project (called The Goulds Belt Distances Survey) designed to provide a detailed view of star-formation in the Solar neighborhood using VLBI observations.
We report on new distances and proper motions to seven stars across the Serpens/Aquila complex. The observations were obtained as part of the Goulds Belt Distances Survey (GOBELINS) project between September 2013 and April 2016 with the Very Long Bas
eline Array (VLBA). One of our targets is the proto-Herbig AeBe object EC 95, which is a binary system embedded in the Serpens Core. For this system, we combined the GOBELINS observations with previous VLBA data to cover a total period of ~8 years, and derive the orbital elements and an updated source distance. The individual distances to sources in the complex are fully consistent with each other, and the mean value corresponds to a distance of $436.0pm9.2$~pc for the Serpens/W40 complex. Given this new evidence, we argue that Serpens Main, W40 and Serpens South are physically associated and form a single cloud structure.
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 Goulds Belt Distances Survey (GOBELINS). We detecte
d 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 $d=129.5pm 0.3$ pc while the B 216 clump in the filamentary structure connected to it is at $d=158.1pm 1.2$ pc. The closest and remotest stars in our sample are located at $d=126.6pm 1.7$ pc and $d=162.7pm 0.8$ 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.
We present results from a high-sensitivity (60 $mu$Jy), large-scale (2.26 square degree) survey obtained with the Karl G. Jansky Very Large Array as part of the Goulds Belt Survey program. We detected 374 and 354 sources at 4.5 and 7.5 GHz, respectiv
ely. Of these, 148 are associated with previously known Young Stellar Objects (YSOs). Another 86 sources previously unclassified at either optical or infrared wavelengths exhibit radio properties that are consistent with those of young stars. The overall properties of our sources at radio wavelengths such as their variability and radio to X-ray luminosity relation are consistent with previous results from the Goulds Belt Survey. Our detections provide target lists for followup VLBA radio observations to determine their distances as YSOs are located in regions of high nebulosity and extinction, making it difficult to measure optical parallaxes.
Recent results indicate the stellar initial mass function is not a strong function of star-forming environment or ``initial conditions (e.g. Meyer et al. 2000). Some studies suggest that a universal IMF may extend to sub-stellar masses (see however B
riceno et al. 2002). Yet most of this work is confined to star-forming environments within 1 kpc of the Sun. In order to probe the universality of the IMF over a wider range of parameter space (metalicity, ambient pressure, magnetic field strength) new techniques are required. We begin by summarizing our approach to deriving the sub-stellar IMF down to the opacity-limit for fragmentation using NGC 1333 as an example. Next, we describe results from simulations using the observed point-spread function of the new 6.5m MMT adaptive optics system and examine the confusion-limited sensitivity to low mass stars in rich star-forming clusters out to 0.5 Mpc. We also present preliminary results from observations with this system of the W51 star-forming complex. Finally, we outline a new technique to estimate the ratio of high to low mass stars in unresolved stellar populations, such as the massive star clusters observed in interacting galaxies (e.g. Mengel et al. 2002). While evidence for variations in the IMF remains inconclusive, new studies are required to rule them out and determine whether or not the IMF is universal over the range of parameter space relevant to star-forming galaxies over cosmic time.
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