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تسجيل مستخدم جديدVLT multi-epoch radial velocity survey toward NGC 6253. Analysis of three transiting planetary candidates
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We measured the radial velocity of 139 stars in the region of NGC 6253, discussing clusters membership and binarity in this sample, complementing our analysis with photometric, proper motion, and radial velocity data available from previous studies of this cluster, and analyzing three planetary transiting candidates we found in the field of NGC 6253. Spectra were obtained with the UVES and GIRAFFE spectrographs at the VLT, during three epochs in August 2008. The mean radial velocity of the cluster is -29.11+/-0.85 km/s. Using both radial velocities and proper motions we found 35 clusters members, among which 12 are likely clusters close binary systems. One star may have a sub-stellar companion, requiring a more intensive follow-up. Our results are in good agreement with past radial velocity and photometric measurements. Furthermore, using our photometry, astrometry and spectroscopy we identified a new sub-giant branch eclipsing binary system, member of the cluster. The clusters close binary frequency at 29% +/- 9% (34% +/-10% once including long period binaries), appears higher than the field binary frequency equal to (22% +/- 5%, though these estimates are still consistent within the uncertainties. Among the three transiting planetary candidates the brightest one (V=15.26) is worth to be more intensively investigated with higher percision spectroscopy. We discussed the possibility to detect sub-stellar companions (brown dwarfs and planets) with the radial velocity technique (both with UVES/GIRAFFE and HARPS) around turn-off stars of old open clusters [abridged].
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The old and metal rich open cluster NGC 6253 was observed with the FLAMES multi-object spectrograph during an extensive radial velocity campaign monitoring 317 stars with a median of 15 epochs per object. All the targeted stars are located along the
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Quasars whose broad emission lines show temporal, bulk radial velocity (RV) shifts have been proposed as candidate sub-parsec (sub-pc), binary supermassive black holes (BSBHs). We identified a sample of 16 BSBH candidates based on two-epoch spectrosc
opy among 52 quasars with significant RV shifts over a few rest-frame years. The candidates showed consistent velocity shifts independently measured from two broad lines (H$beta$ and H$alpha$ or Mg${rm ,II}$) without significant changes in the broad-line profiles. Here in the third paper of the series, we present further third- and fourth-epoch spectroscopy for 12 of the 16 candidates for continued RV tests, spanning $sim$5--15 yr in the quasars rest frames. Cross-correlation analysis of the broad H$beta$ calibrated against [O${rm,III}],lambda 5007$ suggests that 5 of the 12 quasars remain valid as BSBH candidates. They show broad H$beta$ RV curves that are consistent with binary orbital motion without significant changes in the broad line profiles. Their broad H$alpha$ (or Mg${rm ,II}$) lines display RV shifts that are either consistent with or smaller than those seen in broad H$beta$. The RV shifts can be explained by a $sim$0.05--0.1 pc BSBH with an orbital period of $sim$40--130 yr, assuming a mass ratio of 0.5--2 and a circular orbit. However, the parameters are not well constrained given the few epochs that sample only a small portion of the hypothesized binary orbital cycle. The apparent occurrence rate of sub-pc BSBHs is $lesssim$13$pm$5% among all SDSS quasars, with no significant difference in the subsets with and without single-epoch broad line velocity offsets. Dedicated long-term spectroscopic monitoring is still needed to further confirm or reject these BSBH candidates.
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RI photometry. For a smaller region close to the clusters center, we also provide near-infrared JHK photometry. Aims. We analyze the properties of NGC 6253 by using our new photometric data and astrometric membership. Methods. In June 2004, we targeted the cluster during a 10 day multi-site campaign, which involved the MPG/ESO 2.2m telescope with its wide-field imager and the Anglo-Australian 3.9m telescope, equipped with the IRIS2 near-infrared imager. Archival CCD images of NGC 6253 were used to derive relative proper motions and to calculate the cluster membership probabilities. Results. We have refined the clusters fundamental parameters, deriving (V_0-M_v)=11.15, E(B - V)=0.15, E(V - I)=0.25, E(V - J)=0.50, and E(V - H)=0.55. The color excess ratios obtained using both the optical and near infrared colors indicate a normal reddening law in the direction of NGC 6253. The age of NGC 6253 at 3.5 Gyr, determined from our best-fitting isochrone appears to be slightly older than the previous estimates. Finally, we estimated the binary fraction among the cluster members to be sim20%-30% and identified 11 blue straggler candidates.
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