- ID:
- ivo://CDS.VizieR/J/ApJ/709/241
- Title:
- Characterisation of X-rays sources in NGC 6397
- Short Name:
- J/ApJ/709/241
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a deep Chandra X-ray Observatory study of the peculiar binary radio millisecond pulsar (MSP) PSR J1740-5340 and candidate millisecond pulsars in the globular cluster NGC 6397. The X-rays from PSR J1740-5340 appear to be non-thermal and exhibit variability at the binary period. These properties suggest the presence of a relativistic intrabinary shock formed due to interaction of a relativistic rotation-powered pulsar wind and outflow from the unusual "red-straggler/sub-subgiant" companion. We find the X-ray source U18 to show similar X-ray and optical properties to those of PSR J1740-5340, making it a strong MSP candidate. It exhibits variability on timescales from hours to years, also consistent with an intrabinary shock origin of its X-ray emission. The unprecedented depth of the X-ray data allows us to conduct a complete census of MSPs in NGC 6397. Based on the properties of the present sample of X-ray-detected MSPs in the Galaxy, we find that NGC 6397 probably hosts no more than six MSPs.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/764/18
- Title:
- Characteristic frequencies of giant exoplanets
- Short Name:
- J/ApJ/764/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We calculate the eigenfrequencies and eigenfunctions of the acoustic oscillations of giant exoplanets and explore the dependence of the characteristic frequency {nu}_0_ and the eigenfrequencies on several parameters: the planet mass, the planet radius, the core mass, and the heavy element mass fraction in the envelope. We provide the eigenvalues for degree l up to 8 and radial order n up to 12. For the selected values of l and n, we find that the pulsation eigenfrequencies depend strongly on the planet mass and radius, especially at high frequency. We quantify this dependence through the calculation of the characteristic frequency {nu}_0_ which gives us an estimate of the scale of the eigenvalue spectrum at high frequency. For the mass range 0.5M_J_<=M_P_<=15M_J_, and fixing the planet radius to the Jovian value, we find that {nu}_0_~164.0x(M_P_/M_J_)^0.48^{mu}Hz, where M_P_ is the planet mass and M_J_ is Jupiter's mass. For the radius range from 0.9 to 2.0R_J_, and fixing the planet's mass to the Jovian value, we find that {nu}_0_~164.0x(R_P_/R_J_)^-2.09^{mu}Hz, where R_P_ is the planet radius and R_J_ is Jupiter's radius. We explore the influence of the presence of a dense core on the pulsation frequencies and on the characteristic frequency of giant exoplanets. We find that the presence of heavy elements in the envelope affects the eigenvalue distribution in ways similar to the presence of a dense core. Additionally, we apply our formalism to Jupiter and Saturn and find results consistent with both the observational data of Gaulme et al. (2011A&A...531A.104G) and previous theoretical work.
- ID:
- ivo://CDS.VizieR/J/MNRAS/391/1210
- Title:
- Characteristics of energetic pulsars
- Short Name:
- J/MNRAS/391/1210
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we compare the characteristics of pulsars with a high spin-down energy loss rate (Edot) against those with a low Edot. We show that the differences in the total intensity pulse morphology between the two classes are in general rather subtle. A much more significant difference is the fractional polarization which is very high for high Edot pulsars and low for low Edot pulsars. The Edot at the transition is very similar to the death line predicted for curvature radiation. This suggests a possible link between high energy and radio emission in pulsars and could imply that gamma-ray efficiency is correlated with the degree of linear polarization in the radio band. As part of this study, we have discovered three previous unknown interpulse pulsars (and we detected one for the first time at 20cm). We also obtained rotation measures for 18 pulsars whose values had not previously been measured.
- ID:
- ivo://CDS.VizieR/J/AJ/159/281
- Title:
- Characteristics of 335 KOI stars
- Short Name:
- J/AJ/159/281
- Date:
- 09 Dec 2021
- Publisher:
- CDS
- Description:
- We propose several descriptive measures to characterize the arrangements of planetary masses, periods, and mutual inclinations within exoplanetary systems. These measures are based on complexity theory and capture the global, system-level trends of each architecture. Our approach considers all planets in a system simultaneously, facilitating both intrasystem and intersystem analysis. We find that based on these measures, Kepler's high-multiplicity (N>=3) systems can be explained if most systems belong to a single intrinsic population, with a subset of high-multiplicity systems (~20%) hosting additional, undetected planets intermediate in period between the known planets. We confirm prior findings that planets within a system tend to be roughly the same size and approximately coplanar. We find that forward modeling has not yet reproduced the high degree of spacing similarity (in log- period) actually seen in the Kepler data. Although our classification scheme was developed using compact Kepler multis as a test sample, our methods can be immediately applied to any other population of exoplanetary systems. We apply this classification scheme to 1- quantify the similarity between systems, 2- resolve observational biases from physical trends, 3- identify which systems to search for additional planets and where to look for these planets.
- ID:
- ivo://CDS.VizieR/J/MNRAS/505/L79
- Title:
- Characteristic time of stellar flares
- Short Name:
- J/MNRAS/505/L79
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Using the short-cadence data (1-min interval) of the Kepler space telescope, we conducted a statistical analysis for the characteristic time of stellar flares on Sun-like stars (SLS). Akin to solar flares, stellar flares show rise and decay light-curve profiles, which reflect the two distinct phases (rise phase and decay phase) of the flare process. We derived characteristic times of the two phases for the stellar flares of SLS, resulting in a median rise time of about 5.9min and a median decay time of 22.6min. It is found that both the rise time and the decay time of the stellar flares follow a lognormal distribution. The peak positions of the lognormal distributions for flare rise time and decay time are 3.5min and 14.8min, respectively. These time values for stellar flares are similar to the time-scale of solar flares, which supports the idea that stellar flares and solar flares have the same physical mechanism. The statistical results obtained in this work for SLS can be a benchmark of flare characteristic times when comparing with other types of stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/660/1556
- Title:
- Characterization of dusty debris disks
- Short Name:
- J/ApJ/660/1556
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Dusty debris disks around main-sequence stars are signposts for the existence of planetesimals and exoplanets. From cross-correlating Hipparcos stars with the IRAS catalogs, we identify 146 stars within 120pc of Earth that show excess emission at 60um. This search took special precautions to avoid false positives. Our sample is reasonably well distributed from late B to early K-type stars, but it contains very few later type stars. Even though IRAS flew more than 20 years ago and many astronomers have cross-correlated its catalogs with stellar catalogs, we were still able to newly identify debris disks at as many as 33 main-sequence stars; of these, 32 are within 100pc of Earth. The power of an all-sky survey satellite like IRAS is evident when comparing our 33 new debris disks with the total of only 22 dusty debris disk stars first detected with the more sensitive, but pointed, satellite ISO. Our investigation focuses on the mass, dimensions, and evolution of dusty debris disks.
- ID:
- ivo://CDS.VizieR/J/A+A/599/A90
- Title:
- Characterization of HD 108874 system
- Short Name:
- J/A+A/599/A90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In order to understand the observed physical and orbital diversity of extrasolar planetary systems, a full investigation of these objects and of their host stars is necessary. Within this field, one of the main purposes of the GAPS observing project with HARPS-N@TNG is to provide a more detailed characterisation of already known systems. In this framework we monitored the star, hosting two giant planets, HD108874, with HARPS-N for three years in order to refine the orbits, to improve the dynamical study and to search for additional low-mass planets in close orbits. We subtracted the radial velocity (RV) signal due to the known outer planets, finding a clear modulation of 40.2d period. We analysed the correlation between RV residuals and the activity indicators and modelled the magnetic activity with a dedicated code. Our analysis suggests that the 40.2d periodicity is a signature of the rotation period of the star. A refined orbital solution is provided, revealing that the system is close to a mean motion resonance of about 9:2, in a stable configuration over 1Gyr. Stable orbits for low-mass planets are limited to regions very close to the star or far from it. Our data exclude super-Earths with Msini>~5M_{earth}_ within 0.4AU and objects with Msini>~2M_{earth}_ with orbital periods of a few days. Finally we put constraints on the habitable zone of the system, assuming the presence of an exomoon orbiting the inner giant planet.
- ID:
- ivo://CDS.VizieR/J/MNRAS/449/2274
- Title:
- Characterization of Herschel SPIRE FTS
- Short Name:
- J/MNRAS/449/2274
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A systematic programme of calibration observations was carried out to monitor the performance of the Spectral and Photometric Imaging REceiver (SPIRE) Fourier Transform Spectrometer (FTS) instrument on board the Herschel Space Observatory. Observations of planets (including the prime point-source calibrator, Uranus), asteroids, line sources, dark sky and cross-calibration sources were made in order to monitor repeatability and sensitivity, and to improve FTS calibration. We present a complete analysis of the full set of calibration observations and use them to assess the performance of the FTS. Particular care is taken to understand and separate out the effect of pointing uncertainties, including the position of the internal beam steering mirror for sparse observations in the early part of the mission. The repeatability of spectral-line centre positions is <5km/s, for lines with signal-to-noise ratios >40, corresponding to <0.5-2.0 percent of a resolution element. For spectral-line flux, the repeatability is better than 6 percent, which improves to 1-2 percent for spectra corrected for pointing offsets. The continuum repeatability is 4.4 percent for the SPIRE Long Wavelength spectrometer (SLW) band and 13.6 percent for the SPIRE Short Wavelength spectrometer (SSW) band, which reduces to ~1 percent once the data have been corrected for pointing offsets. Observations of dark sky were used to assess the sensitivity and the systematic offset in the continuum, both of which were found to be consistent across the FTS-detector arrays. The average point-source calibrated sensitivity for the centre detectors is 0.20 and 0.21Jy [1{sigma}; 1h], for SLW and SSW. The average continuum offset is 0.40Jy for the SLW band and 0.28Jy for the SSW band.
- ID:
- ivo://CDS.VizieR/J/A+A/475/1125
- Title:
- Characterization of the hot Neptune GJ 436b
- Short Name:
- J/A+A/475/1125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Spitzer Space Telescope infrared photometry of a secondary eclipse as well as ground-based photometric and spectroscopic measurements of the hot Neptune GJ 436b.
- ID:
- ivo://CDS.VizieR/J/ApJ/683/424
- Title:
- CHARA observations of 3 late-type stars
- Short Name:
- J/ApJ/683/424
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the longest baselines of the CHARA Array, we have measured the angular diameter of the G5V subdwarf {mu} Cas A, the first such determination for a halo population star. We compare this result to new diameters for the higher metallicity K0V stars, {sigma} Dra and HR 511, and find that the metal-poor star, {mu} Cas A, has an effective temperature (T_eff_=5297+/-32K), radius (R=0.791+/-0.008R_{sun}_), and absolute luminosity (L=0.442+/-0.014L_{sun}_) comparable to those of the other two stars with later spectral types. We show that stellar models show a discrepancy in the predicted temperature and radius for {mu} Cas A, and we discuss these results and how they provide a key to understanding the fundamental relationships for stars with low metallicity.