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TOPIC: VB 10b
Blobrana


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RE: VB 10b
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Title: Searching for Planets During Predicted Mesolensing Events: I. Theory, and the Case of VB 10
Authors: Rosanne Di Stefano, James Matthews, Sebastien Lepine

The first predicted mesolensing event is likely to occur during the winter or spring of 2011/2012. The lens is the nearby, low-mass high-proper-motion star VB 10, and the source a distant field star much bluer than VB 10 and 1.5 magnitudes dimmer in B band. If VB 10 has planets, they could produce lensing signatures that enhance the detectability of the stellar-lens event and/or produce distinct planet-lens signatures. Here, we study the lensing signatures associated with planets orbiting nearby high-proper-motion stars to provide a guide for observers for this event and future predicted ones. We illustrate our case by considering hypothetical planets orbiting VB 10 with separations ranging from 2 R_{sun} to tens of AU. We find the following. (1) Wide-orbit planets can be detected for all distances of closest approach between the foreground and background stars, potentially producing independent events long before and/or after the closest approach. (2) Close-orbit planets can be detected for intermediate distances of closest approach (less than about 50 mas for VB 10), producing quasiperiodic signatures that may occur days or weeks before and after the stellar-lens event. (3) Planets in the so-called 'zone for resonant lensing' can significantly increase the magnification when the distance of closest approach is small (less than about 20 mas for VB 10), making the stellar-lens event easier to detect while simultaneously providing evidence for planets. We show that an observing plan in which VB 10 is targeted several times per night at each of several longitudes will either detect planets, or else place weak limits on possible parameters. We expect VB 10 to be the first of a continuing line of predicted events. An observing program for this event can pave the way for future programs and discoveries. This is discussed in more detail in Paper II.

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Blobrana


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Posts: 131433
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VB 10
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Title: Searching for Planets During Predicted Mesolensing Events: II. PLAN-IT: An Observing Program and its Application to VB 10
Authors: Rosanne Di Stefano, James Matthews, Sebastien Lepine

The successful prediction of lensing events is a new and exciting enterprise that provides opportunities to discover and study planetary systems. The companion paper investigates the underlying theory. This paper is devoted to outlining the components of observing programs that can discover planets orbiting stars predicted to make a close approach to a background star. If the time and distance of closest approach can be well predicted, then the system can be targeted for individual study. In most cases, however, the predictions will be imprecise, yielding only a set of probable paths of approach and event times. We must monitor an ensemble of such systems to ensure discovery, a strategy possible with observing programs similar to a number of current surveys, including PTF and Pan-STARRS; nova searches, including those conducted by amateurs; ongoing lensing programs such as MOA and OGLE; as well as MEarth, Kepler and other transit studies. If well designed, the monitoring programs will be guaranteed to either discover planets in orbits with semi-major axes smaller than about two Einstein radii, or else to rule out their presence. Planets on wider orbits may not all be discovered, but if they are common, will be found among the events generated by ensembles of potential lenses. We consider the implications for VB 10, the first star to make a predicted approach to a background star that is close enough to allow planets to be discovered. VB 10 is not an ideal case, but it is well worth studying.

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Blobrana


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Title: Astrometric search for a planet around VB 10
Authors: P.F. Lazorenko, J. Sahlmann, D. Segransan, P. Figueira, C. Lovis, E. Martin, M. Mayor, F. Pepe, D. Queloz, F. Rodler, N. Santos, S. Udry

We observed VB 10 in August and September 2009 using the FORS2 camera of the VLT with the aim of measuring its astrometric motion and of probing the presence of the announced planet VB 10b. We used the published STEPS astrometric positions of VB 10 over a time-span of 9 years, which allowed us to compare the expected motion of VB 10 due to parallax and proper motion with the observed motion and to compute precise deviations. The achieved single-epoch precisions of our observations are about 0.1 mas and the data showed no significant residual trend, while the presence of the planet should have induced an apparent proper motion larger than 10 mas/yr. Subtraction of the predicted orbital motion from the observed data produces a large trend in position residuals of VB 10. We estimated the probability that this trend is caused by random noise. Taking all the uncertainties into account and using Monte-Carlo resampling of the data, we are able to reject the existence of VB 10b with the announced mass of 6.4 M_J with the false alarm probability of only 0.0005. A 3.2 M_J planet is also rejected with a false alarm probability of 0.023.

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Blobrana


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Title: Strong Constraints to the Putative Planet Candidate around VB 10 using Doppler spectroscopy
Authors: Guillem Anglada-Escude, Evgenya Shkolnik, Alycia J. Weinberger, Ian B. Thompson, David J. Osip

We present new radial velocity measurements of the ultra-cool dwarf VB 10, which was recently announced to host a giant planet detected with astrometry. The new observations were obtained using optical spectrographs(MIKE/Magellan and ESPaDOnS/CHFT) and cover a 63% of the reported period of 270 days. We apply Least-squares periodograms to identify the most significant signals and evaluate their corresponding False Alarm Probabilities. We show that this method is the proper generalization to astrometric data because (1) it mitigates the coupling of the orbital parameters with the parallax and proper motion, and (2) it permits a direct generalisation to include non-linear Keplerian parameters in a combined fit to astrometry and radial velocity data. In fact, our analysis of the astrometry alone uncovers the reported 270 d period and an even stronger signal at 50 days. We estimate the uncertainties in the parameters using a Markov Chain Monte Carlo approach. The nominal precision of the new Doppler measurements is about 150 s^{-1} while their standard deviation is 250 ms^{-1}. However, the best fit solutions still have RMS of 200 ms^{-1} indicating that the excess in variability is due to uncontrolled systematic errors rather than the candidate companions detected in the astrometry. Although the new data alone cannot rule-out the presence of a candidate, when combined with published radial velocity measurements, the False Alarm Probabilities of the best solutions grow to unacceptable levels strongly suggesting that the observed astrometric wobble is not due to an unseen companion.

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Ground-based astrometry dealt a blow as planet found not to exist.

Strike one planet from the list of 400-odd found around stars in other solar systems: a proposed planet near a star some 6 parsecs from Earth may not exist after all.
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Blobrana


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VB 10
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Title: An Ultracool Star's Candidate Planet
Authors: Steven H. Pravdo, Stuart B. Shaklan

We report here the discovery of the first planet around an ultracool dwarf star. It is also the first extrasolar giant planet (EGP) astrometrically discovered around a main-sequence star. The statistical significance of the detection is shown in two ways. First, there is a 2 x 10^-8 probability that the astrometric motion fits a parallax-and-proper-motion-only model. Second, periodogram analysis shows a false alarm probability of 3 x 10^-5 that the discovered period is randomly generated. The planetary mass is M2 = 6.4 (+2.6,-3.1) Jupiter-masses (MJ), and the orbital period is P = 0.744 (+0.013,-0.008) yr in the most likely model. In less likely models, companion masses that are higher than the 13 MJ planetary mass limit are ruled out by past radial velocity measurements unless the system radial velocity is more than twice the current upper limits and the near-periastron orbital phase was never observed. This new planetary system is remarkable, in part, because its star, VB 10, is near the lower mass limit for a star. Our astrometric observations provide a dynamical mass measurement and will in time allow us to confront the theoretical models of formation and evolution of such systems and their members. We thus add to the diversity of planetary systems and to the small number of known M-dwarf planets. Planets such as VB 10b could be the most numerous type of planets because M stars comprise >70% of all stars. To date they have remained hidden since the dominant radial-velocity (RV) planet-discovery technique is relatively insensitive to these dim, red systems.

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A distant "sun" residing in the constellation Aquila has become the smallest star known to host a planet.
The discovery of a Jupiter-like "exoplanet" orbiting the star VB 10 is the first to be made using the astrometry method.
Astrometry is based on measuring small changes in a star's position.
At one-twelfth the mass of the Sun, VB 10 is tiny; though the star is more massive than its planet, it would have about the same girth, experts say.

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RE: VB 10b
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NASA finds a Jupiter-like planet orbiting a small star.
A long-proposed tool for hunting planets has netted its first catch - a Jupiter-like planet orbiting one of the smallest stars known. The technique, called astrometry, was first attempted 50 years ago to search for planets outside our solar system, called exoplanets. It involves measuring the precise motions of a star on the sky as an unseen planet tugs the star back and forth. But the method requires very precise measurements over long periods of time, and until now, has failed to turn up any exoplanets.
A team of two astronomers from NASA's Jet Propulsion Laboratory, Pasadena, Calif., has, for the past 12 years, been mounting an astrometry instrument to a telescope at the Palomar Observatory near San Diego. After careful, intermittent observations of 30 stars, the team has identified a new exoplanet around one of them - the first ever to be discovered around a star using astrometry.

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Jupiter-Sized Body Is 20 Light-Years Away

This new neighbour is practically next door, as distances in space go. The newfound "exoplanet", called VB 10b, is about 20 light-years away in the constellation Aquila. It is a gas giant, with a mass six times that of Jupiter's, and an orbit far enough away from its star to be labelled a "cold Jupiter" similar to our own. In reality, scientists say, the planet's own internal heat would give it an Earth-like temperature.

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Blobrana


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Van Biesbroeck's Star
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Wolf 1055 AB is also known as Van Biesbroeck's Star (VB 10) after George Van Biesbroeck, who in 1940 detected the faint red dwarf as a companion of the larger, brighter Wolf 1055 A; the system together is Gliese 752.

Source 

Position(2000): RA 19 16 55.3, Dec  +05 10 11

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Blobrana


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Posts: 131433
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RE: VB 10b
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The tiny star known as VB 10 is located 20 light years away in the constellation Aquila and is now the smallest star known to have an exoplanet. The planet, VB 10b, is six times more massive than Jupiter, but just about the same size as Jupiter.
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