- ID:
- ivo://CDS.VizieR/J/other/RNAAS/5.13
- Title:
- CHEOPS limb and gravity-darkening coefficients
- Short Name:
- J/other/RNAAS/5.
- Date:
- 17 Jan 2022 00:43:02
- Publisher:
- CDS
- Description:
- The goal of this Research Note is to provide the theoretical calculations of the limb-darkening coefficients (LDC) and gravity-darkening coefficients (GDC) for the space mission CHEOPS. We use two stellar atmosphere models: ATLAS (plane-parallel) and PHOENIX with spherical symmetry covering a wide range of effective temperatures, local gravities, and hydrogen/metal. These grids cover 19 metallicities ranging from 10^-5^ up to 10^+1^ solar abundances, 0<=logg<=6.0 and 2300K<=Te<=50000K. The specific intensity distribution was fitted using six approaches: linear, quadratic, square root, logarithmic, power-2, and a series with four terms. The calculations of the gravity darkening coefficient were performed for both stellar atmosphere models adopting an improved formulation.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/659/A74
- Title:
- CHEOPS phase curve of WASP-189 b
- Short Name:
- J/A+A/659/A74
- Date:
- 10 Mar 2022 06:44:26
- Publisher:
- CDS
- Description:
- Gas giants orbiting close to hot and massive early-type stars can reach dayside temperatures that are comparable to those of the coldest stars. These "ultra-hot Jupiters" have atmospheres made of ions and atomic species from molecular dissociation and feature strong day-to-night temperature gradients. Photometric observations at different orbital phases provide insights on the planet atmospheric properties. We analyse the photometric observations of WASP-189 acquired with the instrument CHEOPS to derive constraints on the system architecture and the planetary atmosphere. We implement a light curve model suited for asymmetric transit shape caused by the gravity-darkened photosphere of the fast-rotating host star. We also model the reflective and thermal components of the planetary flux, the effect of stellar oblateness and light-travel time on transit-eclipse timings, the stellar activity and CHEOPS systematics. From the asymmetric transit, we measure the size of the ultra-hot Jupiter WASP-189, R_p_=1.600_-0.016_^+0.017^R_J_, with a precision of 1%, and the true orbital obliquity of the planetary system {Psi}_p_=89.6+/-1.2deg (polar orbit). We detect no significant hotspot offset from the phase curve and obtain an eclipse depth {delta}_ecl_=96.5_-5.0_^+4.5^ppm, from which we derive an upper limit on the geometric albedo: A_g_<0.48. We also find that the eclipse depth can only be explained by thermal emission alone in the case of extremely inefficient energy redistribution. Finally, we attribute the photometric variability to the stellar rotation, either through superficial inhomogeneities or resonance couplings between the convective core and the radiative envelope. Based on the derived system architecture, we predict the eclipse depth in the upcoming TESS observations to be up to ~165ppm. High-precision detection of the eclipse in both CHEOPS and TESS passbands might help disentangle between reflective and thermal contributions. We also expect the right ascension of the ascending node of the orbit to precess due to the perturbations induced by the stellar quadrupole moment J_2_ (oblateness).
- ID:
- ivo://CDS.VizieR/J/A+A/657/A52
- Title:
- CHEOPS transit light curves of WASP-103 b
- Short Name:
- J/A+A/657/A52
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Ultra-short period planets undergo strong tidal interactions with their host star which lead to planet deformation and orbital tidal decay. WASP-103b is the exoplanet with the highest expected deformation signature in its transit light curve and one of the shortest expected spiral-in times. Measuring the tidal deformation of the planet would allow us to estimate the second degree fluid Love number and gain insight into the planet's internal structure. Moreover, measuring the tidal decay timescale would allow us to estimate the stellar tidal quality factor, which is key to constraining stellar physics. We obtained 12 transit light curves of WASP-103b with the CHaracterising ExOplanet Satellite (CHEOPS) to estimate the tidal deformation and tidal decay of this extreme system. We modelled the high-precision CHEOPS transit light curves together with systematic instrumental noise using multi-dimensional Gaussian process regression informed by a set of instrumental parameters. To model the tidal deformation, we used a parametrisation model which allowed us to determine the second degree fluid Love number of the planet. We combined our light curves with previously observed transits of WASP-103b with the Hubble Space Telescope (HST) and Spitzer to increase the signal-to-noise of the light curve and better distinguish the minute signal expected from the planetary deformation. We estimate the radial Love number of WASP-103b to be h_f_=1.59+/-0.53 This is the first time that the tidal deformation is directly detected (at 3 sigma) from the transit light curve of an exoplanet. Combining the transit times derived from CHEOPS, HST, and Spitzer light curves with the other transit times available in the literature, we find no significant orbital period variation for WASP-103b. However, the data show a hint of an orbital period increase instead of a decrease, as is expected for tidal decay. This could be either due to a visual companion star if this star is bound, the Applegate effect, or a statistical artefact. The estimated Love number of WASP-103b is similar to Jupiters. This will allow us to constrain the internal structure and composition of WASP-103b, which could provide clues on the inflation of hot Jupiters. Future observations with James Webb Space Telescope (JWST) can better constrain the radial Love number of WASP-103b due to their high signal-to-noise and the smaller signature of limb darkening in the infrared. A longer time baseline is needed to constrain the tidal decay in this system.
- ID:
- ivo://CDS.VizieR/J/A+A/643/A94
- Title:
- CHEOPS WASP-189 b transit light curve
- Short Name:
- J/A+A/643/A94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- CHEOPS (CHaracterising ExOPlanets Satellite), launched in December 2019, is a space mission dedicated to exoplanet follow-up with the capacity to perform photometric measurements at the20 ppm level. As CHEOPS observes in a broad optical passband, it can be used provide insights on the reflected light from exoplanets, and constrain the short-wavelength thermal emission for the hottest of planets through the observation of occultations and phase curves. We here report the first observation of an occultation by CHEOPS: that of the hot Jupiter WASP-189b, a M~2M_J_ planet orbiting an A-type star. We detect the occultation of WASP-189b at high significance in individual measurements, and derive an occultation depth of dF=87.9+/-4.3 ppm based on four occultations. We compare this measurement to model predictions and find that, when assuming inefficient heat redistribution, they are consistent with an unreflective atmosphere, heated to a temperature of 3435+/-27K. We furthermore present two transits of WASP-189b observed by CHEOPS. These transits have an asymmetric shape that we attribute to gravity darkening of the host star due to its high rotation rate. We use these measurements to refine the planetary parameters, finding a ~25% deeper transit compared to the discovery paper and updating the radius of WASP-189b to 1.619+/-0.021R_J_. We further measure the projected orbital obliquity to be lambda=86.4(+2.9,-4.4)deg, a value in good agreement with a previous measurement from spectroscopic observations, and derive a true obliquity of Psi=85.4+/-4.3deg. Finally, we provide reference values for the photometric precision attained by the CHEOPS satellite: for the V=6.6 mag star, and using a 1-hour binning, we obtain a residual RMS between 10 and 17ppm on the individual light curves, and 5.7ppm when combining four visits.
- ID:
- ivo://CDS.VizieR/J/ApJ/806/268
- Title:
- Cheshire Cat galaxies: redshifts and magnitudes
- Short Name:
- J/ApJ/806/268
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Cheshire Cat is a relatively poor group of galaxies dominated by two luminous elliptical galaxies surrounded by at least four arcs from gravitationally lensed background galaxies that give the system a humorous appearance. Our combined optical/X-ray study of this system reveals that it is experiencing a line of sight merger between two groups with a roughly equal mass ratio with a relative velocity of ~1350 km/s. One group was most likely a low-mass fossil group, while the other group would have almost fit the classical definition of a fossil group. The collision manifests itself in a bimodal galaxy velocity distribution, an elevated central X-ray temperature and luminosity indicative of a shock, and gravitational arc centers that do not coincide with either large elliptical galaxy. One of the luminous elliptical galaxies has a double nucleus embedded off-center in the stellar halo. The luminous ellipticals should merge in less than a Gyr, after which observers will see a massive 1.2-1.5x10^14^ M_{sun}_ fossil group with an M_r_=-24.0 brightest group galaxy at its center. Thus, the Cheshire Cat offers us the first opportunity to study a fossil group progenitor. We discuss the limitations of the classical definition of a fossil group in terms of magnitude gaps between the member galaxies. We also suggest that if the merging of fossil (or near-fossil) groups is a common avenue for creating present-day fossil groups, the time lag between the final galactic merging of the system and the onset of cooling in the shock-heated core could account for the observed lack of well-developed cool cores in some fossil groups.
- ID:
- ivo://CDS.VizieR/J/ApJ/765/156
- Title:
- CH(G) index of SDSS evolved stars
- Short Name:
- J/ApJ/765/156
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have measured the CH G band (CH(G)) index for evolved stars in the globular cluster M3 based on the Sloan Digital Sky Survey (SDSS) spectroscopic survey. It is found that there is a useful way to select red giant branch (RGB) stars from the contamination of other evolved stars such as asymptotic giant branch (AGB) and red horizontal branch (RHB) stars by using the CH(G) index versus (g-r)_0_ diagram if the metallicity is known from the spectra. When this diagram is applied to field giant stars with similar metallicity, we establish a calibration of CH(G)=1.625(g-r)_0_-1.174(g-r)^2^_0_-0.934. This method is confirmed by stars with [Fe/H]~-2.3 where spectra of member stars in globular clusters M15 and M92 are available in the SDSS database. We thus extend this kind of calibration to every individual metallicity bin ranging from [Fe/H]~-3.0 to [Fe/H]~0.0 by using field red giant stars with 0.4<=(g-r)_0_<=1.0. The metallicity-dependent calibrations give CH(G)=1.625(g-r)_0_-1.174(g-r)^2^_0_+0.060[Fe/H]-0.830 for -3.0<[Fe/H]<=-1.2 and CH(G)=0.953(g-r)_0_-0.655(g-r)^2^_0_+0.060[Fe/H]-0.650 for -1.2<[Fe/H]<0.0. The calibrations are valid for the SDSS spectroscopic data set, and they cannot be applied blindly to other data sets. With the two calibrations, a significant number of the contaminating stars (AGB and RHB stars) were excluded and thus a clear sample of red giant stars is obtained by selecting stars within +/-0.05mag of the calibration. The sample is published online and it is expected that this large and clean sample of RGB stars will provide new information on the formation and evolution of the Galaxy.
- ID:
- ivo://CDS.VizieR/J/ApJS/212/13
- Title:
- ChIcAGO. I. Sample and initial results
- Short Name:
- J/ApJS/212/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the Chasing the Identification of ASCA Galactic Objects (ChIcAGO) survey, which is designed to identify the unknown X-ray sources discovered during the ASCA Galactic Plane Survey (AGPS). Little is known about most of the AGPS sources, especially those that emit primarily in hard X-rays (2-10keV) within the F_x_~10^-13^ to 10^-11^erg/cm2/s X-ray flux range. In ChIcAGO, the subarcsecond localization capabilities of Chandra have been combined with a detailed multiwavelength follow-up program, with the ultimate goal of classifying the >100 unidentified sources in the AGPS. Overall to date, 93 unidentified AGPS sources have been observed with Chandra as part of the ChIcAGO survey. A total of 253 X-ray point sources have been detected in these Chandra observations within 3' of the original ASCA positions. We have identified infrared and optical counterparts to the majority of these sources, using both new observations and catalogs from existing Galactic plane surveys. X-ray and infrared population statistics for the X-ray point sources detected in the Chandra observations reveal that the primary populations of Galactic plane X-ray sources that emit in the F_x_~10^-13^ to 10^-11^ erg/cm2/s flux range are active stellar coronae, massive stars with strong stellar winds that are possibly in colliding wind binaries, X-ray binaries, and magnetars. There is also another primary population that is still unidentified but, on the basis of its X-ray and infrared properties, likely comprises partly Galactic sources and partly active galactic nuclei.
- ID:
- ivo://CDS.VizieR/J/PASP/122/347
- Title:
- Chinese Small Telescope ARray (CSTAR)
- Short Name:
- J/PASP/122/347
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In 2008 January the twenty-fourth Chinese expedition team successfully deployed the Chinese Small Telescope ARray (CSTAR) to Dome A, the highest point on the Antarctic plateau. CSTAR consists of four 14.5cm optical telescopes, each with a different filter (g,r,i, and open) and has a 4.5{deg}x4.5{deg} field of view (FOV). It operates robotically as part of the Plateau Observatory, PLATO, with each telescope taking an image every ~30s throughout the year whenever it is dark. During 2008, CSTAR 1 performed almost flawlessly, acquiring more than 0.3 million -band images for a total integration time of 1728hr during 158 days of observations. For each image taken under good sky conditions, more than 10,000 sources down to magnitude could be detected. We performed aperture photometry on all the sources in the field to create the catalog described herein. Since CSTAR has a fixed pointing centered on the south celestial pole (Dec=-90{deg}), all the sources within the FOV of CSTAR were monitored continuously for several months. The photometric catalog can be used for studying any variability in these sources, and for the discovery of transient sources such as supernovae, gamma-ray bursts, and minor planets.
- ID:
- ivo://CDS.VizieR/J/A+A/658/A198
- Title:
- CHIPS II. O stars in Trumpler 14 CHIPS-Tr14
- Short Name:
- J/A+A/658/A198
- Date:
- 25 Feb 2022 07:07:49
- Publisher:
- CDS
- Description:
- Most massive stars belong to multiple systems, yet the formation process leading to such high multiplicity remain insufficiently understood. To help constrain the different formation scenarios that exist, insights on the low-mass end of the companion mass function of such stars is crucial. However, this is a challenging endeavour as (sub-)solar mass companions at angular separations {rho} below 1" (corresponding to 1000-3000au in nearby young open clusters and OB associations) are difficult to detect due to the large brightness contrast with the central star. With the Carina High-contrast Imaging Project of massive Stars (CHIPS), we aim to obtain statistically significant constraints on the presence and properties of low-mass companions around massive stars at a previously unreachable observing window ({Delta}mag>=10 at {rho}<= 1"). In this second paper in the series, we focus on the Trumpler 14 cluster, which harbours some of the youngest and most massive O-type stars in the Milky Way. We obtained VLT-SPHERE observations of seven O-type objects in Trumpler 14 using the IRDIFS_EXT mode. These allow us to search for companions at separations larger than 0.15" (~360au) and down to magnitude contrast >10 mag in the near-infrared. We used angular and spectral differential imaging along with PSF fitting to detect sources and measure their flux relative to that of the central object. We detected 211 sources with near-infrared magnitude contrast in the range of 2 to 12. The closest companion, at only 0.26", is characterised as a 1.4M_{sun}_ stars with an age of 0.6Myr, in excellent agreement with previous age estimates for Tr14. The mass function peaks at about 0.4M_{sun}_ and presents a dearth of stars in the 0.5 to 0.8M_{sun}_ mass range compared to previous estimates of the initial mass function in Tr14.
- ID:
- ivo://CDS.VizieR/J/A+A/641/A110
- Title:
- Chromospheric activity of nearby Sun-like stars
- Short Name:
- J/A+A/641/A110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The chromospheric emission in the cores of the CaII H & K lines of late-type dwarfs is a well known indicator of magnetic activity that decreases with increasing stellar age. I use this indicator to investigate the formation history of nearby G- and early K-type stars with origins at galactocentric distances similar to that of the region where the Sun was born. A parent sample of single main-sequence stars with near-solar metallicity and known magnetic activity levels is built from catalogues of stellar atmospheric parameters and chromospheric activity indices. A kinematical approach uses Gaia astrometric data to differentiate thin disc stars from thick disc stars. Measured distributions of R'_HK_ chromospheric activity indices are compared with Monte Carlo simulations based on an empirical model of chromospheric activity evolution. The thin disc includes a significant fraction of Sun-like stars with intermediate activity levels while most early K- and G-type stars from the thick disc are inactive. The chromospheric activity distribution among nearby Sun-like dwarfs from the thin disc can be explained by a combination of an old (>6-7Gyr) star formation event (or events) and a more recent (<3Gyr) burst of star formation. Such an event is not required to account for the R'_HK_ index distributions of nearby thick disc stars. The distribution of magnetic activity among local G- and early K-type stars with a near-solar metallicity bears the imprint of an important star formation event that occurred ~1.9 to 2.6Gyr ago in the thin disc of the Milky Way.
