We present a comprehensive photometric analysis of a young open cluster NGC 1960 (= M36) along with the long-term variability study of this cluster. Based on the kinematic data of Gaia DR2, the membership probabilities of 3871 stars are ascertained in the cluster field among which 262 stars are found to be cluster members. Considering the kinematic and trigonometric measurements of the cluster members, we estimate a mean cluster parallax of 0.86±0.05 mas and mean proper motions of µ RA = -0.143±0.008 mas yr −1 , µ Dec = -3.395±0.008 mas yr −1 . We obtain basic parameters of the cluster such as E(B − V) = 0.24±0.02 mag, log(Age/yr)=7.44±0.02, and d = 1.17±0.06 kpc. The mass function slope in the cluster for the stars in the mass range of 0.72-7.32 M ⊙ is found to be γ = -1.26±0.19. We find that mass segregation is still taking place in the cluster which is yet to be dynamically relaxed. This work also presents first high-precision variability survey in the central 13 ′ × 13 ′ region of the cluster. The V band photometric data accumulated on 43 nights over a period of more than 3 years reveals 76 variable stars among which 72 are periodic variables. Among them, 59 are short-period (P < 1 day)and 13 are long-period (P > 1 day). The variable stars have V magnitudes ranging between 9.1 to 19.4 mag and periods between 41 minutes to 10.74 days. On the basis of their locations in the H-R diagram, periods and characteristic light curves, the 20 periodic variables belong to the cluster. We classified them as 2 δ-Scuti, 3 γ-Dor, 2 slowly pulsating B stars, 5 rotational variables, 2 non-pulsating B stars and 6 as miscellaneous variables.
Measured spectral shifts due to intrinsic stellar variability (e.g., pulsations, granulation) and activity (e.g., spots, plages) are the largest source of error for extreme-precision radial-velocity (EPRV) exoplanet detection. Several methods are designed to disentangle stellar signals from true center-of-mass shifts due to planets. The Extreme-precision Spectrograph (EXPRES) Stellar Signals Project (ESSP) presents a self-consistent comparison of 22 different methods tested on the same extreme-precision spectroscopic data from EXPRES. Methods derived new activity indicators, constructed models for mapping an indicator to the needed radial-velocity (RV) correction, or separated out shape- and shift-driven RV components. Since no ground truth is known when using real data, relative method performance is assessed using the total and nightly scatter of returned RVs and agreement between the results of different methods. Nearly all submitted methods return a lower RV rms than classic linear decorrelation, but no method is yet consistently reducing the RV rms to sub-meter-per-second levels. There is a concerning lack of agreement between the RVs returned by different methods. These results suggest that continued progress in this field necessitates increased interpretability of methods, high-cadence data to capture stellar signals at all timescales, and continued tests like the ESSP using consistent data sets with more advanced metrics for method performance. Future comparisons should make use of various well-characterized data sets—such as solar data or data with known injected planetary and/or stellar signals—to better understand method performance and whether planetary signals are preserved.
This work presents the first long-term photometric variability survey of the intermediate-age open cluster NGC 559. Time-series V band photometric observations on 40 nights taken over more than three years with three different telescopes are analyzed to search for variable stars in the cluster. We investigate the data for the periodicity analysis and reveal 70 variable stars including 67 periodic variables in the target field, all of them are newly discovered. The membership analysis of the periodic variables reveal that 30 of them belong to the cluster and remaining 37 are identified as field variables. Out of the 67 periodic variables, 48 are short-period (P < 1 day) variables and 19 are long-period (P > 1 day) variables. The variable stars have periodicity between 3 hours to 41 days and their brightness ranges from V = 10.9 to 19.3 mag. The periodic variables belonging to the cluster are then classified into different variability types on the basis of observational properties such as shape of the light curves, periods, amplitudes, as well as their positions in the Hertzsprung-Russell (H-R) diagram. As a result, we identify one Algol type eclipsing binary, one possible blue straggler star, 3 slowly pulsating B type stars, 5 rotational variables, 11 non-pulsating variables, 2 FKCOM variables and remaining 7 are characterized as miscellaneous variables. We also identify three Eclipsing Binary stars (EBs) belonging to the field star population. The PHOEBE package is used to analyse the light curve of all four EBs in order to determine the parameters of the binary systems such as masses, temperatures and radii.
CoRoT-7 is an active star, whose orbiting planets and their masses have been under debate since their initial detection. In the previous studies, CoRoT-7 was found to have two planets, CoRoT-7b and CoRoT-7c with orbital periods 0.85 and 3.69 d, and a potential third planet with a period ∼9 d. The existence of the third planet has been questioned later as potentially being an activity-induced artefact. Moreover, mass of the transiting planet CoRoT-7b has been estimated to have widely different values owing to the activity level of the parent star, the consequent RV ‘jitter’, and the methods used to rectify this ambiguity. Here. we present an analysis of the HARPS archival RV (RV) data of CoRoT-7 using a new wavelength-domain technique, scalpels, to correct for the stellar activity-induced spectral line-shape changes. Simultaneous modelling of stellar activity and orbital motions, identified using the ℓ1- periodogram, shows that scalpels effectively reduce the contribution of stellar variability to the RV signal and enhance the detectability of exoplanets around active stars. Using kima nested-sampling package (Faria et al.), we modelled the system incorporating a Gaussian Process together with scalpels. The resultant posterior distributions favoured a three-planet system comprising two non-transiting planets, CoRoT-7c and CoRoT-7d with orbital periods 3.697 ± 0.005 and 8.966 ± 1.546 d, in addition to the known transiting planet. The transiting planet CoRoT-7b is found to be a rocky super-Earth with a mass of Mb = 6.06 ± 0.65M⊕. The determined masses of Mc = 13.29 ± 0.69M⊕ and Md = 17.14 ± 2.55M⊕ suggest the non-transiting planets CoRoT-7c and CoRoT-7d to be structurally similar to Uranus and Neptune.
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