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- ID:
- ivo://CDS.VizieR/J/ApJ/876/59
- Title:
- Chandra X-ray sources in the globular cluster 47 Tuc
- Short Name:
- J/ApJ/876/59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using archival Chandra observations with a total exposure of 510ks, we present an updated catalog of point sources for globular cluster (GC) 47 Tucanae. Our study covers an area of ~176.7'^2^ (i.e., with R<~7.5') with 537 X-ray sources. We show that the surface density distribution of X-ray sources in 47 Tuc is highly peaked in the cluster center, rapidly decreases at intermediate radii, and finally rises again at larger radii, with two distribution dips at R~100" and R~170" for the faint (L_X_>~5.0x10^30^erg/s) and bright (L_X_<~5.0x10^30^erg/s) groups of X-ray sources, respectively. These distribution features are similar to those of blue straggler stars (BSSs), where the distribution dip is located at R~200". By fitting the radial distribution of each group of sources with a "generalized King model", we estimated an average mass of 1.51+/-0.17M_{sun}_, 1.44+/-0.15M_{sun}_ and 1.16+/-0.06M_{sun}_ for the BSSs, bright X-ray sources, and faint X-ray sources, respectively. These results are consistent with the mass segregation effect of heavy objects in GCs, where more massive objects drop to the cluster center faster and their distribution dip propagates outward further. Besides, the peculiar distribution profiles of X-ray sources and BSSs are also consistent with the mass segregation model of binaries in GCs, which suggests that, in addition to the dynamical formation channel, primordial binaries are also a significant contributor to the X-ray source population in GCs.
- ID:
- ivo://CDS.VizieR/J/ApJ/591/138
- Title:
- Chandra X-ray sources of NGC 1068
- Short Name:
- J/ApJ/591/138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of the compact X-ray source population in the Seyfert 2 galaxy NGC 1068, imaged with a 50ks Chandra observation. We find a total of 84 compact sources on the S3 chip, of which 66 are located within the 25.0B-mag/arcsec^2^ isophote of the galactic disk of NGC 1068. Spectra have been obtained for the 21 sources with at least 50 counts and modeled with both multicolor disk blackbody and power-law models.
- ID:
- ivo://CDS.VizieR/J/ApJ/736/90
- Title:
- Chandra X-ray sources of NGC 1399
- Short Name:
- J/ApJ/736/90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a wide-field study of the globular cluster (GC)/low-mass X-ray binary (LMXB) connection in the giant elliptical NGC 1399. The large field of view of the Advanced Camera for Surveys/WFC, combined with Hubble Space Telescope and Chandra high resolution, allow us to constrain the LMXB formation scenarios in elliptical galaxies. We confirm that NGC 1399 has the highest LMXB fraction in GCs of all nearby elliptical galaxies studied so far, even though the exact value depends on galactocentric distance due to the interplay of a differential GC versus galaxy light distribution and the GC color dependence. In fact, LMXBs are preferentially hosted by bright, red GCs out to >5R_eff_ of the galaxy light. The finding that GCs hosting LMXBs follow the radial distribution of their parent GC population argues against the hypothesis that the external dynamical influence of the galaxy affects the LMXB formation in GCs. On the other hand, field-LMXBs closely match the host galaxy light, thus indicating that they are originally formed in situ and not inside GCs. We measure GC structural parameters, finding that the LMXB formation likelihood is influenced independently by mass, metallicity, and GC structural parameters. In particular, the GC central density plays a major role in predicting which GCs host accreting binaries. Finally, our analysis shows that LMXBs in GCs are marginally brighter than those in the field, and in particular the only color-confirmed GC with L_X_>10^39^erg/s shows no variability, which may indicate a superposition of multiple LMXBs in these systems.
- ID:
- ivo://CDS.VizieR/J/ApJ/589/225
- Title:
- Chandra X-ray sources toward Galactic Center
- Short Name:
- J/ApJ/589/225
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of 2357 point sources detected during 590ks of Chandra observations of the 17x17' field around Sgr A*. This field encompasses a physical area of 40x40pc at a distance of 8kpc. The completeness limit of the sample at the Galactic center is 10^31^erg/s (2.0-8.0keV), while the detection limit is an order of magnitude lower. The 281 sources detected below 1.5keV are mainly in the foreground of the Galactic center, while comparisons to the Chandra deep fields at high Galactic latitudes suggest that only about 100 of the observed sources are background AGNs.
- ID:
- ivo://CDS.VizieR/J/AJ/150/81
- Title:
- CHANG-ES. IV. VLA D-configuration observations
- Short Name:
- J/AJ/150/81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first part of the observations made for the Continuum Halos in Nearby Galaxies, an EVLA Survey (CHANG-ES) project. The aim of the CHANG-ES project is to study and characterize the nature of radio halos, their prevalence as well as their magnetic fields, and the cosmic rays illuminating these fields. This paper reports observations with the compact D configuration of the Karl G. Jansky Very Large Array (VLA) for the sample of 35 nearby edge-on galaxies of CHANG-ES. With the new wide bandwidth capabilities of the VLA, an unprecedented sensitivity was achieved for all polarization products. The beam resolution is an average of 9.6" and 36" with noise levels reaching approximately 6 and 30{mu}Jy/beam for C- and L-bands, respectively (robust weighting). We present intensity maps in these two frequency bands (C and L), with different weightings, as well as spectral index maps, polarization maps, and new measurements of star formation rates (SFRs). The data products described herein are available to the public in the CHANG-ES data release available at http://www.queensu.ca/changes. We also present evidence of a trend among galaxies with larger halos having higher SFR surface density, and we show, for the first time, a radio continuum image of the median galaxy, taking advantage of the collective signal-to-noise ratio of 30 of our galaxies. This image shows clearly that a "typical" spiral galaxy is surrounded by a halo of magnetic fields and cosmic rays.
- ID:
- ivo://CDS.VizieR/J/ApJ/893/96
- Title:
- CHAOS IV: NGC3184 LBT obs. & 3 other gal. abundances
- Short Name:
- J/ApJ/893/96
- Date:
- 07 Mar 2022 07:28:28
- Publisher:
- CDS
- Description:
- The chemical abundances of spiral galaxies, as probed by HII regions across their disks, are key to understanding the evolution of galaxies over a wide range of environments. We present Large Binocular Telescope/Multi-Object Double Spectrographs spectra of 52 HII regions in NGC 3184 as part of the CHemical Abundances Of Spirals (CHAOS) project. We explore the direct-method gas-phase abundance trends for the first four CHAOS galaxies, using temperature measurements from one or more auroral-line detections in 190 individual HII regions. We find that the dispersion in T_e_-T_e_ relationships is dependent on ionization, as characterized by F_{lambda}5007_/F_{lambda}3727_, and so we recommend ionization-based temperature priorities for abundance calculations. We confirm our previous results that [NII] and [SIII] provide the most robust measures of electron temperature in low-ionization zones, while [OIII] provides reliable electron temperatures in high-ionization nebula. We measure relative and absolute abundances for O, N, S, Ar, and Ne. The four CHAOS galaxies marginally conform with a universal O/H gradient, as found by empirical integral field unit studies when plotted relative to effective radius. However, after adjusting for vertical offsets, we find a tight universal N/O gradient of {alpha}_N/O_=-0.33dex/R_e_ with {sigma}_tot._=0.08 for R_g_/R_e_<2.0, where N is dominated by secondary production. Despite this tight universal N/O gradient, the scatter in the N/O-O/H relationship is significant. Interestingly, the scatter is similar when N/O is plotted relative to O/H or S/H. The observable ionic states of S probe lower ionization and excitation energies than O, which might be more appropriate for characterizing abundances in metal-rich HII regions.
- ID:
- ivo://CDS.VizieR/J/ApJ/858/71
- Title:
- CHARA array obs. of 13 AB Dor moving group stars
- Short Name:
- J/ApJ/858/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present interferometric measurements obtained with the CHARA Array of 13 adolescent-age stars in nearby moving groups. The motivation was to spatially resolve the largest stars and to search for binary companions. Nine stars have diameters smaller than the resolution limit and no evidence for companions within 0.5-50mas and {Delta}H<2.0mag. The diameters of three stars were spatially resolved: GJ 159 (0.582+/-0.016mas) and GJ 393 (0.564+/-0.021mas) in the AB Dor moving group, and former member HD 89744 (0.556+/-0.032mas). Combining the angular diameters with their distances and bolometric fluxes, we measured radii and effective temperatures. The temperatures of GJ 159 (6286+/-123K) and GJ 393 (3515+/-68K) are consistent with spectroscopic measurements. Comparisons with evolutionary models show that HD 89744 has evolved off the main sequence. GJ 159 and GJ 393 lie within 1.5{sigma} of the zero-age main sequence, complicating their age estimates because it is unclear whether the stars are contracting or expanding. GJ 159 has a mass of 1.2+/-0.1M_{sun}_ with an age spanning 0.021-3.0Gyr. Its debris disk and lithium abundance favor a young age. GJ 393 has a mass of 0.42+/-0.03M_{sun}_ and a lower limit on its age 0.06Gyr. This overlaps with the age of the moving group; however, an older age would be more consistent with its slow rotation, low activity, and luminosity, suggesting that GJ 393 is a kinematic interloper.
- 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.
- 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.