- ID:
- ivo://CDS.VizieR/J/ApJ/872/17
- Title:
- HAZMAT. V. UV and X-ray evolution of K stars
- Short Name:
- J/ApJ/872/17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Knowing the high-energy radiation environment of a star over a planet's formation and evolutionary period is critical in determining if that planet is potentially habitable and if any biosignatures could be detected, as UV radiation can severely change or destroy a planet's atmosphere. Current efforts for finding a potentially habitable planet are focused on M stars, yet K stars may offer more habitable conditions due to decreased stellar activity and more distant and wider habitable zones (HZs). While M star activity evolution has been observed photometrically and spectroscopically, there has been no dedicated investigation of K star UV evolution. We present the first comprehensive study of the near-UV, far-UV, and X-ray evolution of K stars. We used members of young moving groups and clusters ranging in age from 10 to 625Myr combined with field stars and their archived GALEX UV and ROSAT X-ray data to determine how the UV and X-ray radiation evolve. We find that the UV and X-ray flux incident on an HZ planet is 5-50 times lower than that of HZ planets around early-M stars and 50-1000 times lower than those around late-M stars, due to both an intrinsic decrease in K dwarf stellar activity occurring earlier than for M dwarfs and the more distant location of the K dwarf HZ.
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- ID:
- ivo://CDS.VizieR/J/A+A/403/493
- Title:
- H-band observation of Chandra Deep Field South
- Short Name:
- J/A+A/403/493
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report preliminary results of our H-band survey of the Chandra Deep Field South (CDFS). The observations were made using SofI on the NTT, and cover 0.027 square degrees with a 50% completeness limit of H=20.5, and 0.17 square degrees with a 50% completeness limit of H=19.8. We used SExtractor to extract sources from our fields. In total we have detected 4819 objects. Star-galaxy separation was performed using the SExtractor parameter "stellarity index". All objects with an index of 0.5 or lower were classified as galaxies. According to this criterion, 80% of our detections are galaxies. We then compare our results with previous observations of the CDFS. Our astrometric solutions are in good agreement with the Las Campanas Infrared Survey (LCIRS), the COMBO-17 and the ESO-EIS surveys. The photometry of our catalog compares satisfactorily with the results of the LCIRS, as well as with the GOODS data. Galaxy number counts are presented and compared with the LCIRS results. The present data are intended to complement the recent and future multi-wavelength observations of the CDFS and will be used, in conjunction with additional multiband photometry, to find counterparts of the upcoming mid-infrared surveys with SIRTF.
- ID:
- ivo://CDS.VizieR/J/A+A/414/905
- Title:
- H-band photometry in Pisces-Perseus disk galaxies
- Short Name:
- J/A+A/414/905
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the scaling relations of bulge and disk structural parameters for a sample of 108 disk galaxies. Structural parameters of individual galaxies are obtained from two-dimensional bulge/disk decomposition of their H-band surface brightness distributions. Bulges are modelled with a generalized exponential (Sersic) with variable integer shape index n.
- ID:
- ivo://CDS.VizieR/J/A+AS/137/101
- Title:
- H-band photometry in Pisces-Perseus spirals
- Short Name:
- J/A+AS/137/101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The paper presents results of an H-band imaging survey of spiral galaxies in the Perseus-Pisces supercluster area. The derived global photometric parameters of the sample galaxies (magnitudes, diameters, etc.) are collected in Table 3.
- ID:
- ivo://CDS.VizieR/J/ApJ/796/64
- Title:
- H{beta} and Ly{alpha} emitting galaxies at z~2
- Short Name:
- J/ApJ/796/64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compare the H{beta} line strengths of 1.90<z<2.35 star-forming galaxies observed with the near-IR grism of the Hubble Space Telescope with ground-based measurements of Ly{alpha} from the HETDEX Pilot Survey and narrow-band imaging. By examining the line ratios of 73 galaxies, we show that most star-forming systems at this epoch have a Ly{alpha} escape fraction below ~6%.
- ID:
- ivo://CDS.VizieR/J/ApJ/847/136
- Title:
- H{beta} to N2 line fluxes of nearby galaxies
- Short Name:
- J/ApJ/847/136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present calibrations for star formation rate (SFR) indicators in the ultraviolet, mid-infrared, and radio-continuum bands, including one of the first direct calibrations of 150MHz as an SFR indicator. Our calibrations utilize 66 nearby star-forming galaxies with Balmer-decrement-corrected H{alpha} luminosities, which span five orders of magnitude in SFR and have absolute magnitudes of -24<M_r_{<}-12. Most of our photometry and spectrophotometry are measured from the same region of each galaxy, and our spectrophotometry has been validated with SDSS photometry, so our random and systematic errors are small relative to the intrinsic scatter seen in SFR indicator calibrations. We find that the Wide-field Infrared Space Explorer W4 (22.8{mu}m), Spitzer 24{mu}m, and 1.4GHz bands have tight correlations with the Balmer-decrement-corrected H{alpha} luminosity, with a scatter of only 0.2dex. Our calibrations are comparable to those from the prior literature for L* galaxies, but for dwarf galaxies, our calibrations can give SFRs that are far greater than those derived from most previous literature.
- ID:
- ivo://CDS.VizieR/J/ApJ/821/113
- Title:
- HCG and RSCG compact group galaxies with WISE
- Short Name:
- J/ApJ/821/113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Compact groups provide an environment to study the growth of galaxies amid multiple prolonged interactions. With their dense galaxy concentrations and relatively low velocity dispersions, compact groups mimic the conditions of hierarchical galaxy assembly. Compact group galaxies are known to show a bimodality in Spitzer IRAC infrared color space: galaxies are preferentially either quiescent with low specific star formation rates (SSFRs) or prolifically forming stars-galaxies with moderate levels of specific star formation are rare. Previous Spitzer IRAC studies identifying this "canyon" have been limited by small number statistics. We utilize whole-sky Wide-field Infrared Survey Explorer (WISE) data to study 163 compact groups, thereby tripling our previous sample and including more galaxies with intermediate mid-IR colors indicative of moderate SSFRs. We define a distinct WISE mid-IR color space (log[f_12_/f_4.6_]) versus (log[f_22_/f_3.4_]) that we use to identify canyon galaxies from the larger sample. We confirm that compact group galaxies show a bimodal distribution in the mid-infrared and identify 37 canyon galaxies with reliable photometry and intermediate mid-IR colors. Morphologically, we find that the canyon harbors a large population of both Sa-Sbc and E/S0 type galaxies, and that they fall on the optical red sequence rather than the green valley. Finally, we provide a catalog of WISE photometry for 567 of 652 galaxies selected from the sample of 163 compact groups.
- ID:
- ivo://CDS.VizieR/J/ApJ/903/111
- Title:
- HCN, HNC, H13CN & HC3N of Galactic Center map. II.
- Short Name:
- J/ApJ/903/111
- Date:
- 15 Mar 2022
- Publisher:
- CDS
- Description:
- We report a statistical analysis exploring the origin of the overall low star formation efficiency (SFE) of the Galactic central molecular zone (CMZ) and the SFE diversity among the CMZ clouds using a wide-field HCN J=4-3 map, whose optically thin critical density (~10^7^/cm^3^) is the highest among the tracers ever used in CMZ surveys. Logistic regression is performed to empirically formulate star formation probability of 195 HCN clumps, 13 of which contain star formation signatures. The explanatory parameters in the best-fit model are reduced into the virial parameter {alpha}_vir_ without significant contribution from other parameters, whereas the performance of the model without {alpha}_vir_ is no better than that using randomly generated data. The threshold {alpha}_vir_ is 6, which translates into a volume density (n_H_2__) of 10^4.6^/cm^3^ with the n_H_2__-{alpha}_vir_ correlation. The scarcity of the low-{alpha}_vir_ clumps, whose fraction to all HCN clumps is 0.1, can be considered as one of the immediate causes of the suppressed SFE. No correlation between the clump size or mass and star formation probability is found, implying that HCN J= 4-3 does not immediately trace the mass of star-forming gas above a threshold density. Meanwhile, star-forming and non-star-forming clouds are degenerate in the physical parameters of the CS J=1-0 clouds, highlighting the efficacy of the HCN J=4-3 line to probe star-forming regions in the CMZ. The timescale of the high-{alpha}_vir_ to low-{alpha}_vir_ transition is <~2Myr, which is consistent with the tidal compression and X1/X2 orbit transition models but possibly does not fit the cloud-cloud collision picture.
- ID:
- ivo://CDS.VizieR/J/A+A/633/A154
- Title:
- HDBSCAN star, galaxy, QSO classification
- Short Name:
- J/A+A/633/A154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Classification will be an important first step for upcoming surveys that will detect billions of new sources such as LSST and Euclid, as well as DESI, 4MOST and MOONS. The application of traditional methods of model fitting and colour-colour selections will face significant computational constraints, while machine-learning (ML) methods offer a viable approach to tackle datasets of that volume. While supervised learning methods can perform very well for classification tasks, the creation of representative and accurate training sets is a resource and time consuming task. We present a viable alternative using an unsupervised ML method to separate stars, galaxies and QSOs using photometric data. The heart of our work uses HDBSCAN to find the star, galaxy and QSO clusters in a multidimensional colour space. We optimized the hyperparameters and input attributes of three separate HDBSCAN runs, each to select a particular object class, and thus treat the output of each separate run as a binary classifier. We subsequently consolidate the output to give our final classifications, optimized on their F1 scores. We explore the use of Random Forest and PCA as part of the pre-processing stage for feature selection and dimensionality reduction. Using our dataset of ~50000 spectroscopically labelled objects we obtain an F1 score of 98.9, 98.9 and 93.13 respectively for star, galaxy and QSO selection using our unsupervised learning method. We find that careful attribute selection is a vital part of accurate classification with HDBSCAN. We applied our classification to a subset of the SDSS spectroscopic catalogue and demonstrate the potential of our approach in correcting misclassified spectra useful for DESI and 4MOST. Finally, we create a multiwavelength catalogue of 2.7 million sources using the KiDS, VIKING and ALLWISE surveys and publish corresponding classifications and photometric redshifts.
- ID:
- ivo://CDS.VizieR/J/A+A/646/A157
- Title:
- HD 108236 CHEOPS light curves
- Short Name:
- J/A+A/646/A157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The detection of a super-Earth and three mini-Neptunes transiting the bright (V=9.2mag) star HD108236 (also known as TOI-1233) was recently reported on the basis of TESS and ground-based light curves. We perform a first characterisation of the HD108236 planetary system through high-precision CHEOPS photometry and improve the transit ephemerides and system parameters. We characterise the host star through spectroscopic analysis and derive the radius with the infrared flux method.We constrain the stellar mass and age by combining the results obtained from two sets of stellar evolutionary tracks. We analyse the available TESS light curves and one CHEOPS transit light curve for each known planet in the system. We find that HD108236 is a Sun-like star with R*=0.877+/-0.008R_{sun}_, M*=0.869^+0.050^_0.048_M_{sun}_, and an age of 6.7^+4.0^_5.1_Gyr. We report the serendipitous detection of an additional planet, HD108236 f, in one of the CHEOPS light curves. For this planet, the combined analysis of the TESS and CHEOPS light curves leads to a tentative orbital period of about 29.5days. From the light curve analysis, we obtain radii of 1.615+/-0.051, 2.071+/-0.052, 2.539^+0.062^_0.065_, 3.083+/-0.052, and 2.017^+0.052^+0.057_R_{Earth}_ for planets HD108236 b to HD108236 f, respectively. These values are in agreement with previous TESS-based estimates, but with an improved precision of about a factor of two. We perform a stability analysis of the system, concluding that the planetary orbits most likely have eccentricities smaller than 0.1. We also employ a planetary atmospheric evolution framework to constrain the masses of the five planets, concluding that HD108236 b and HD108236 c should have an Earth-like density, while the outer planets should host a low mean molecular weight envelope. The detection of the fifth planet makes HD108236 the third system brighter than V=10mag to host more than four transiting planets. The longer time span enables us to significantly improve the orbital ephemerides such that the uncertainty on the transit times will be of the order of minutes for the years to come. A comparison of the results obtained from the TESS and CHEOPS light curves indicates that for a V~9mag solar-like star and a transit signal of 500ppm, one CHEOPS transit light curve ensures the same level of photometric precision as eight TESS transits combined, although this conclusion depends on the length and position of the gaps in the light curve.
