* Astronomy

Blobrana · L

RE: Messier 67

Blobrana · L

M67 was discovered sometime before 1779 by German astronomer Johann Gottfried Koehler. He described the cluster as being rather conspicuous and nebula like in appearance although with his basic telescope, he was unable to resolve it into stars. Charles Messier then independently rediscovered M67, resolved it into stars and catalogued it on April 6, 1780 as a "Cluster of small stars with nebulosity, below the southern claw of Cancer. The position determined from the star Alpha [Cancri].".
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Blobrana · L

Title: Search for giant planets in M67 I. Overview
Authors: L. Pasquini, A. Brucalassi, M. T. Ruiz, P. Bonifacio, C. Lovis, R. Saglia, C. Melo, K. Biazzo, S. Randich, L. R. Bedin

Precise stellar radial velocities are used to search for massive (Jupiter masses or higher) exoplanets around the stars of the open cluster M67. We aim to obtain a census of massive exoplanets in a cluster of solar metallicity and age in order to study the dependence of planet formation on stellar mass and to compare in detail the chemical composition of stars with and without planets. This first work presents the sample and the observations, discusses the cluster characteristics and the radial velocity (RV) distribution of the stars, and individuates the most likely planetary host candidates. We observed a total of 88 main-sequence stars, subgiants, and giants all highly probable members of M67, using four telescopes and instrument combinations. We investigate whether exoplanets are present by obtaining radial velocities with precisions as good as 10 m/s. To date, we have performed 680 single observations (Dec. 2011) and a preliminary analysis of data, spanning a period of up to eight years. Although the sample was pre-selected to avoid the inclusion of binaries, we identify 11 previously unknown binary candidates. Eleven stars clearly displayed larger RV variability and these are candidates to host long-term substellar companions. The average RV is also independent of the stellar magnitude and evolutionary status, confirming that the difference in gravitational redshift between giants and dwarfs is almost cancelled by the atmospheric motions. We use the subsample of solar-type stars to derive a precise true RV for this cluster. We finally create a catalogue of binaries and use it to clean the colour magnitude diagram (CMD). As conclusion, by pushing the search for planets to the faintest possible magnitudes, it is possible to observe solar analogues in open clusters, and we propose 11 candidates to host substellar companions.

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Blobrana · L

Title: Lithium in M67: from the main sequence to the red giant branch
Authors: Giancarlo Pace, Matthieu Castro, Jorge Melendez, Sylvie Theado, Jose-Dias do Nascimento Jr

Lithium abundances in open clusters are a very effective probe of mixing processes, and their study can help to understand the large depletion of lithium in the Sun. Due to its age and metallicity, the open cluster M67 is especially interesting on this regard. Many studies on lithium abundances in M67 have already been performed, but a homogeneous global analysis of lithium in stars from subsolar up to the most massive members, was never accomplished for a large sample based on high-quality spectra. We tested our non-standard models, which were calibrated using the Sun with observational data. We collected literature data to follow, for the first time in a homogeneous way, NLTE lithium abundances of all observed single stars in M67 more massive than about 0.9 solar masses. Our grid of evolutionary models were computed with non-standard mixing at metallicity [Fe/H] = 0.01, using the Toulouse-Geneva evolution code. The analysis is started from the entrance in the ZAMS. Lithium in M67 is a tight function of mass for stars more massive than the Sun, apart of a few outliers. A plateau in lithium abundances is observed for turn-off stars. Both less massive and more massive stars are more depleted than those in the plateau. There is a significant scatter in lithium abundances for any given mass lower than M <= 1.1 solar masses. Our models qualitatively reproduce most of the features described above, although the predicted depletion of lithium is 0.45 dex smaller than observed for masses in the plateau region, i.e. between 1.1 and 1.28 solar masses. Clearly, more work is needed to thoroughly match the observations. Despite hints that chromospheric activity and rotation play a role in lithium depletion, no firm conclusion can be drawn with the presently available data.

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Blobrana · L

Title: Deep 2MASS Photometry of M67 and Calibration of the Main Sequence J-Ks Colour Difference as an Age Indicator
Authors: Ata Sarajedini, Aaron Dotter, Allison Kirkpatrick

We present an analysis of Two Micron All Sky Survey (2MASS) calibration photometry of the old open cluster M67 (NGC 2682). The proper motion-cleaned colour-magnitude diagram (CMD) resulting from these data extends ~3 magnitudes deeper than one based on data from the point source catalogue. The CMD extends from above the helium-burning red clump to a faint limit that is more than 7 magnitudes below the main sequence turnoff in the Ks band. After adopting a reddening of E(B-V) = 0.041 ±0.004 and a metal abundance of [Fe/H] = -0.009 ±0.009 based on a survey of published values, we fit the unevolved main sequence of M67 to field main sequence stars with 2MASS photometry and Hipparcos parallaxes. This analysis yields distance moduli of (m-M)Ks = 9.72 ±0.05 and (m-M)o = 9.70 ±0.05, which are consistent with published values. We compare the theoretical isochrones of Girardi et al. and Dotter et al. to the CMD of M67 and comment on the relative merits of each set of models. These comparisons suggest an age between 3.5 and 4.0 Gyr for M67. The depth of the M67 data make them ideal for the calibration of a new age indicator that has recently been devised by Calamida et al.- the difference in (J-Ks) colour between the main sequence turnoff (TO) and the point on the lower main sequence where it turns down (TD) and becomes nearly vertical [D(J-Ks)]. Coupled with deep 2MASS photometry for three other open clusters, NGC 2516, M44, and NGC 6791, we calibrate D(J-Ks) in terms of age and find D(J-Ks) = (3.017 ±0.347) - (0.259 ±0.037)*Log Age (yrs).

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