A Photometric Search for Planets in the Open Cluster NGC 7086 (original) (raw)

A search for planets in the old open cluster NGC 6791

Astronomy & Astrophysics, 2003

We describe the results of a search for transit-like events caused by giant planets occulting stars in the old, metal-rich open cluster NGC 6791 based on BVI-colour photometry from eight nights of observations with the 2.54m Nordic Optical Telescope. To extract the light curves we have used both PSF photometry (DAOPHOT) and the difference imaging technique (ISIS). We have re-analyzed observations from earlier campaigns to search for multiple transits, determine periods of long-period variables, and detect eclipsing binaries. We confirm 20 known variables and have discovered 22 new low-amplitude variables with amplitudes in the range 7--40 mmag and periods 1--16 days. We have found the primary and secondary eclipses of two eclipsing binaries based on the new and older photometric campaigns. The search for transits-like events has turned up a few single-transit candidates. The transit depths are 10 mmag in both the V and I filters over periods of 1.0--2.5 hours, but future observations are required to see whether identical transit-like events recur in these same stars.

Photometric study and detection of variable stars in the open clusters - I. NGC 6866

Monthly Notices of the Royal Astronomical Society, 2012

We present results of a variability search in the intermediate-age open cluster NGC 6866 from 29 nights over two observing seasons. We find 28 periodic variables, of which 19 are newly identified. The periods of these variables, which have V magnitudes from 11.5 to 19.3 mag, range from ∼ 48 min to 37 d. We detected several δ-Scuti stars, some of which are of high amplitude, as well as γ-Doradus, rotational variables and eclipsing binaries. In order to study the physical properties of the cluster, we obtained U BV RI photometry of all the stars on a good photometric night. The radial distribution of the stellar surface density shows that the cluster has a radial extent of about 7 arcmin (∼ 3 pc) with a peak density of 5.7 ± 0.7 stars/arcmin 2 at the cluster center. The colour-colour diagram indicates a reddening of E(B − V ) = 0.10 mag towards NGC 6866. A distance of ∼1.47 kpc and an age of ∼ 630 Myr is estimated from the colour-magnitude diagram using the theoretical isochrones of solar metallicity.

A new search for planet transits in NGC 6791

Astronomy and Astrophysics, 2007

Context. Searching for planets in open clusters allows us to study the effects of dynamical environment on planet formation and evolution. Aims. Considering the strong dependence of planet frequency on stellar metallicity, we studied the metal rich old open cluster NGC 6791 and searched for close-in planets using the transit technique. Methods. A ten-night observational campaign was performed using the Canada-France-Hawaii Telescope (3.6m), the San Pedro Mártir telescope (2.1m), and the Loiano telescope (1.5m). To increase the transit detection probability we also made use of the Bruntt et al. eight-nights observational campaign. Adequate photometric precision for the detection of planetary transits was achieved. Results. Should the frequency and properties of close-in planets in NGC 6791 be similar to those orbiting field stars of similar metallicity, then detailed simulations foresee the presence of 2-3 transiting planets. Instead, we do not confirm the transit candidates proposed by . The probability that the null detection is simply due to chance coincidence is estimated to be 3%-10%, depending on the metallicity assumed for the cluster. Conclusions. Possible explanations of the null-detection of transits include: (i) a lower frequency of close-in planets in star clusters; (ii) a smaller planetary radius for planets orbiting super metal rich stars; or (iii) limitations in the basic assumptions. More extensive photometry with 3-4m class telescopes is required to allow conclusive inferences about the frequency of planets in NGC 6791.

Searching for planetary transits in the field of open cluster NGC 6819–I

Monthly Notices of …, 2003

We present results from our survey for planetary transits in the field of the intermediate age (∼2.5 Gyr), metal-rich ([Fe/H]∼+0.07) open cluster NGC 6819. We have obtained highprecision time-series photometry for over 38,000 stars in this field and have developed an effective matched-filter algorithm to search for photometric transits. This algorithm identified 8 candidate stars showing multiple transit-like events, plus 3 stars with single eclipses. On closer inspection, while most are shown to be low mass stellar binaries, some of these events could be due to brown dwarf companions. The data for one of the single-transit candidates indicates a minimum radius for the companion similar to that of HD 209458b.

Kepler observations of the open cluster NGC 6819

Using photometry from the Kepler Input Catalogue, we determine the distance and age of NGC 6819 using several different methods. From isochrone fitting we find the age of the cluster to be about 2.5 Gyr. There are many different types of variables in the field, including eight δ Scuti stars, at least three γ Dor variables and several eclipsing binaries of various types. We derive masses, radii and luminosities from 63 red giants with solar-like oscillations, including 28 stars with no previous measurements, from which we obtain an unreddened distance modulus of 12.20 ± 0.06 mag. We measured rotation periods of 129 stars which showed variations attributable to starspots. There is a correlation between the rotation period and the colour which extends to stars with temperatures equivalent to late A-type. This implies that starspots are present in stars which are much hotter than previously supposed. We also discuss several eclipsing binaries and the variability of stars which are blue straggler candidates and discuss X-ray sources found in the cluster.

A Photometric and Astrometric Study of the Open Clusters NGC 1664 and NGC 6939

Astronomical Journal, 2022

This study calculated astrophysical parameters, as well as kinematic and galactic orbital parameters, of the open clusters NGC 1664 and NGC 6939. The work is based on CCD ultraviolet, blue, and visual (UBV) and Gaia photometric and astrometric data from ground-and space-based observations. Considering Gaia Early Data Release 3 (EDR3) astrometric data, we determined membership probabilities of stars located in both of the clusters. We used two-color diagrams to determine the E(B − V) color excesses for NGC 1664 and NGC 6939 as 0.190 ± 0.018 and 0.380 ± 0.025 mag, respectively. Photometric metallicities for the two clusters were estimated as [Fe/H] = −0.10 ± 0.02 dex for NGC 1664 and as [Fe/H] = −0.06 ± 0.01 dex for NGC 6939. Using the reddening and metallicity calculated in the study, we obtained distance moduli and ages of the clusters by fitting PARSEC isochrones to the color-magnitude diagrams based on the most likely member stars. Isochrone fitting distances are 1289 ± 47 pc and 1716 ± 87 pc, which coincide with ages of 675 ± 50 Myr and 1.5 ± 0.2 Gyr for NGC 1664 and NGC 6939, respectively. We also derived the distances to the clusters using Gaia trigonometric parallaxes and compared these estimates with the literature. We concluded that the results are in good agreement with those given by the current study. Present-day mass function slopes were calculated as Γ = −1.22 ± 0.33 and Γ = −1.18 ± 0.21 for NGC 1664 and NGC 6939, respectively, which are compatible with the Salpeter slope. Analyzes showed that both of clusters are dynamically relaxed. The kinematic and dynamic orbital parameters of the clusters were calculated, indicating that the birthplaces of the clusters are outside the solar circle.

A photometric and radial-velocity analysis of the intermediate-age open cluster NGC 752

Publications of the Astronomical Society of the Pacific, 1994

Using all available proper-motion and radial-velocity data, including new radial-velocity observations obtained for this investigation, probable members of the open cluster NGC 752 have been identified. Photoelectric data on six systems have been transformed and collated to form an internally consistent sample on the BVsystem. Binaries have been identified using photometric and radial-velocity data, including a photographic survey for variability and the radial-velocity observations of this study. Analysis of the data leads to the following cluster parameters and their probable errors: E(B-V) =0.035±0.005 mag, [Fe/H]=-0.15±0.05 dex, and (m-Af) = 8.25±0.10 mag. The spread in color among stars in the color-magnitude diagram (cmd) along the main sequence from the turnoff to the unevolved main sequence is the consequence of a rich population of binaries. Due to its age and the comprehensive data available for the cluster, NGC 752 provides an ideal test of a variety of evolutionary phenomena. Comparison with theoretical isochrones normalized in an internally consistent manner leads to the conclusion that the morphology and distribution of stars in the cmd can best be matched using models that include convective overshoot, particularly those of Schaller et al. (1992, A&AS, 96, 269). Despite their differences, the traditional and the overshoot isochrones both imply very similar ages, 1.9 ±0.2 Gyr and 1.7 ±0.1 Gyr, respectively, for the cluster. The Li abundances for the giants confirm that the giant branch is dominated by clump stars and first-ascent giants below the luminosity of the clump. The position and size of the Li dip among the main-sequence stars, compared to the Hyades, is readily explained by stellar evolution with convective overshoot. It is predicted that among turnoff stars in the intermediate-age range Li will cease to be a unique function of age at a given color. Chromospheric flux is shown to be a well-defined function of color for single, unevolved stars, identical to that found for the Hyades, and the relation for NGC 752 falls within the Vaughan-Preston gap. However, the slope of the relation requires that increasing color implies increasing age for the bluer portion of the weak-emission boundary. The combined effect of small samples, random errors, emission limits, a possible selection bias in favor of turnoff stars, and metallicity corrections is to render highly questionable any interpretation of time-variable star formation within the Galaxy based upon chromospheric ages.

A survey for planetary transits in the field of NGC 7789

Monthly Notices of the Royal Astronomical Society, 2005

We present results from 30 nights of observations of the open cluster NGC 7789 with the WFC camera on the INT telescope in La Palma. From ∼900 epochs, we obtained lightcurves and Sloan r ′ − i ′ colours for ∼33000 stars, with ∼2400 stars with better than 1% precision. We expected to detect ∼2 transiting hot Jupiter planets if 1% of stars host such a companion and that a typical hot Jupiter radius is ∼ 1.2R J . We find 24 transit candidates, 14 of which we can assign a period. We rule out the transiting planet model for 21 of these candidates using various robust arguments. For 2 candidates we are unable to decide on their nature, although it seems most likely that they are eclipsing binaries as well. We have one candidate exhibiting a single eclipse for which we derive a radius of 1.81 +0.09 −0.00 R J . Three candidates remain that require follow-up observations in order to determine their nature.

Bright Variable Stars in NGC 6819 - An Open Cluster in the Kepler Field

The Astronomical Journal

We describe a variability study of the moderately old open cluster NGC 6819. We have detected 4 new detached eclipsing binaries near the cluster turnoff (one of which may be in a triple system). Several of these systems should be able to provide mass and radius information, and can therefore constrain the age of the cluster. We have also newly detected one possible detached binary member about 3.5 magnitudes below the turnoff. One EW-type binary (probably not a cluster member) shows unusually strong night-to-night light curve variations in sets of observations separated by 8 years. According to the best current information, the three brightest variables we detected (2 of them new) are cluster members, making them blue stragglers. One is a delta Scu pulsating variable, one is a close but detached binary, and the third contains a detached short period binary that shows total eclipses. In each case, however, there is evidence hinting that the system may have been produced through the i...

An HST search for planets in the lower main sequence of the globular cluster NGC 6397

Astronomy & Astrophysics, 2012

Searches for planetary transits carried out in open and globular clusters have to date yielded only a handful of weak, unconfirmed candidates. These results have been interpreted as either being insignificant, or evidence that the cluster chemical or dynamical environment inhibits planetary formation or survival. Most campaigns have been limited by small sample statistics or systematics from ground-based photometry. We performed a search for transiting planets and variables in a deep stellar field of NGC 6397 imaged by HST-ACS over 126 orbits. We analyzed 5078 light curves, including a careful selection of 2215 cluster-member M0-M9 dwarfs. The light curves were corrected for systematic trends and inspected using several tools. No high-significance planetary candidate is detected. We compared this null detection with the most recent results from Kepler, showing that no conclusive evidence of lower planet incidence can be drawn. However, a very small photometric jitter is measured for early-M cluster members (2 mmag on 98% of them), which may be worth targeting in the near future with more optimized campaigns. Twelve variable stars are reported for the first time.