Y. C. Joshi

Multi-site campaign for transit timing variations of WASP-12 b: possible detection of a long-period signal of planetary origin

Aims. The transiting planet WASP-12 b was identified as a potential target for transit-timing studies because a departure from a linear ephemeris has been reported in the literature. Such deviations could be caused by an additional planet in the system. We attempt to confirm the claimed variations in transit timing and interpret their origin. Methods. We organised a multi-site campaign to observe transits by WASP-12 b in three observing seasons, using 0.5–2.6-metre telescopes. Results. We obtained 61 transit light curves, many of them with sub-millimagnitude precision. The simultaneous analysis of the best-quality datasets allowed us to obtain refined system parameters, which agree with values reported in previous studies. The residuals versus a linear ephemeris reveal a possible periodic signal that may be approximated by a sinusoid with an amplitude of 0.00068 ± 0.00013 d and period of 500 ± 20 orbital periods of WASP-12 b. The joint analysis of timing data and published radial velocity measurements results in a two-planet model that explains observations better than do single-planet scenarios. We hypothesise that WASP-12 b might not be the only planet in the system, and there might be the additional 0.1 MJup body on a 3.6-d eccentric orbit. A dynamical analysis indicates that the proposed two-planet system is stable on long timescales.

Study of open clusters within 1.8 kpc and understanding the Galactic structure

Based on an almost complete sample of Galactic open star clusters within 1.8 kpc, we perform a comprehensive statistical analysis of various cluster parameters like spatial position, age, size, mass and extinction in order to understand the general properties of the open cluster system in the Galaxy and the Galactic structure. Based on the distribution of 1241 open clusters about the Galactic plane and in different age bins, we find the average Galactic scale height as Zh = 60+/-2 pc for the youngest cluster population having Age <700 Myr, however, it increases up to 64+/-2 pc when we also include older population of clusters. The solar offset is found to be 6.2+/-1.1 pc above the formal Galactic plane. We derive a local mass density of \rho_0 = 0.090+/-0.005 Msun/pc^3 and found a negligibly small amount of dark matter in the solar neighbourhood. The reddening in the direction of clusters suggests a strong correlation with their vertical distance from the Galactic plane having a respective slope of dE(B-V)/dz = 0.40+/-0.04 and 0.42+/-0.05 mag/kpc below and above the GP. We observe a linear mass-radius and mass-age relations in the open clusters and derive a slope of dR/d(logM) = 2.08+/-0.10 and d(logM)/d(logT) = -0.36+/-0.05,respectively.

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

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 and rotational variables, and eclipsing binaries. In order to study the physical properties of the cluster, we obtained UBVRI 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 centre. 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 are estimated from the colour–magnitude diagram using the theoretical isochrones of solar metallicity.

The hot γ Doradus and Maia stars

The hot

Photometric study of two novae in M 31

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Photometric study of the open cluster – II. Stellar population and dynamical evolution in NGC 559

~Doradus stars have multiple low frequencies characteristic of

The Nainital-Cape Survey - IV. A search for pulsational variability in 108 chemically peculiar stars

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Basic Parameters of Open Star Clusters DOLIDZE 14 and NGC 110 in Infrared bands

~Dor or SPB variables, but are located between the red edge of the SPB and the blue edge of the

A spectroscopic analysis of the chemically peculiar star HD207561

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Investigation of open clusters based on IPHAS and APASS survey data

~Dor instability strips where all low-frequency modes are stable in current models of these stars. Though