- ID:
- ivo://CDS.VizieR/J/AJ/162/72
- Title:
- Random forests method to discover high-redshift QSOs
- Short Name:
- J/AJ/162/72
- Date:
- 14 Mar 2022 07:01:17
- Publisher:
- CDS
- Description:
- We present a method of selecting quasars up to redshift ~6 with random forests, a supervised machine-learning method, applied to Pan-STARRS1 and WISE data. We find that, thanks to the increasing set of known quasars, we can assemble a training set that enables supervised machine-learning algorithms to become a competitive alternative to other methods up to this redshift. We present a candidate set for the redshift range 4.8-6.3, which includes the region around z=5.5 where selecting quasars is difficult due to their photometric similarity to red and brown dwarfs. We demonstrate that, under our survey restrictions, we can reach a high completeness (66%{+/-}7% below redshift 5.6/83_-9_^+6^% above redshift 5.6) while maintaining a high selection efficiency (78_-8_^+10^%/94_-8_^+5^% ). Our selection efficiency is estimated via a novel method based on the different distributions of quasars and contaminants on the sky. The final catalog of 515 candidates includes 225 known quasars. We predict the candidate catalog to contain additional 148_-33_^+41^ new quasars below redshift 5.6 and 45_-8_^+5^ above, and we make the catalog publicly available. Spectroscopic follow-up observations of 37 candidates led us to discover 20 new high redshift quasars (18 at 4.6<~z<~5.5, 2z~5.7). These observations are consistent with our predictions on efficiency. We argue that random forests can lead to higher completeness because our candidate set contains a number of objects that would be rejected by common color cuts, including one of the newly discovered redshift 5.7 quasars.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/294/135
- Title:
- Rapid variations of Eta Cen
- Short Name:
- J/A+A/294/135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/A+A/602/A53
- Title:
- R Aqr SPHERE/ZIMPOL narrow-H{alpha} image
- Short Name:
- J/A+A/602/A53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- R Aqr is a symbiotic binary system consisting of a mira variable, a hot companion with a spectacular jet outflow, and an extended emission line nebula. Because of its proximity to the Sun, this object has been studied in much detail with many types of high resolution imaging and interferometric techniques. We have used R Aqr as test target for the visual camera subsystem ZIMPOL, which is part of the new extreme adaptive optics (AO) instrument SPHERE at the Very Large Telescope (VLT). We describe SPHERE/ZIMPOL test observations of the R Aqr system taken in H{alpha} and other filters in order to demonstrate the exceptional performance of this high resolution instrument. We compare our observations with data from the Hubble Space Telescope (HST) and illustrate the complementarity of the two instruments. We use our data for a detailed characterization of the inner jet region of R Aqr. We analyze the high resolution ~=25mas images from SPHERE/ZIMPOL and determine from the H{alpha} emission the position, size, geometric structure, and line fluxes of the jet source and the clouds in the innermost region <2"(<400AU) of R Aqr. The data are compared to simultaneous HST line filter observations. The H{alpha} fluxes and the measured sizes of the clouds yield H{alpha} emissivities for many clouds from which one can derive the mean density, mass, recombination time scale, and other cloud parameters. Our H{alpha} data resolve for the first time the R Aqr binary and we measure for the jet source a relative position 45 mas West (position angle -89.5{deg}) of the mira. The central jet source is the strongest H{alpha} component with a flux of about 2.5x10^-12^erg/cm^2^/s. North east and south west from the central source there are many clouds with very diverse structures. Within 0.5" (100AU) we see in the SW a string of bright clouds arranged in a zig-zag pattern and, further out, at 1"-2", fainter and more extended bubbles. In the N and NE we see a bright, very elongated filamentary structure between 0.2"-0.7" and faint perpendicular "wisps" further out. Some jet clouds are also detected in the ZIMPOL [OI] and HeI filters, as well as in the HST-WFC3 line filters for H{alpha}, [OIII], [NII], and [OI]. We determine jet cloud parameters and find a very well defined correlation Ne{prop.to}r^-1.3^ between cloud density and distance to the central binary. Densities are very high with typical values of Ne~=3x10^5^cm^-3^ for the "outer" clouds around 300AU, Ne~=3x10^6^cm^-3^ for the "inner" clouds around 50AU, and even higher for the central jet source. The high Ne of the clouds implies short recombination or variability timescales of a year or shorter. H{alpha} high resolution data provide a lot of diagnostic information for the ionized jet gas in R Aqr. Future H{alpha} observations will provide the orientation of the orbital plane of the binary and allow detailed hydrodynamical investigations of this jet outflow and its interaction with the wind of the red giant companion.
- ID:
- ivo://CDS.VizieR/J/A+AS/146/323
- Title:
- RASS young sources around R CrA
- Short Name:
- J/A+AS/146/323
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the ROSAT All-Sky Survey data in a 126 deg^2^ area in and around the CrA star forming region. With low-resolution spectroscopy of unidentified ROSAT sources we could find 19 new pre-main sequence stars, two of which are classical T Tauri stars, the others being weak-lined. The spectral types of these new T Tauri stars range from F7 to M6. The two new classical T Tauri stars are located towards two small cloud-lets outside of the main CrA cloud. They appear to be ~10 Myrs old, by comparing their location in the H-R diagram with isochrones for an assumed distance of 130 pc, the distance of the main CrA dark cloud. The new off-cloud weak-line T Tauri stars may have formed in similar cloudlets, which have dispersed recently. High-resolution spectra of our new T Tauri stars show that they have significantly more lithium absorption than zero-age main-sequence stars of the same spectral type, so that they are indeed young. From those spectra we also obtained rotational and radial velocities. For some stars we found the proper motion in published catalogs. The direction and velocity of the 3D space motion - south relative to the galactic plane - of the CrA T Tauri stars is consistent with the dark cloud being formed originally by a high-velocity cloud impact onto the galactic plane, which triggered the star formation in CrA. We also present VRIJHK photometry for most of the new T Tauri stars to derive their luminosities, ages, and masses.
- ID:
- ivo://CDS.VizieR/J/ApJ/897/78
- Title:
- RAVE J183013.5-455510 equivalent-width measurements
- Short Name:
- J/ApJ/897/78
- Date:
- 15 Mar 2022 04:12:46
- Publisher:
- CDS
- Description:
- We report on the spectroscopic analysis of RAVE-J183013.5-455510, an extremely metal-poor star, highly enhanced in CNO, and with discernible contributions from the rapid neutron-capture process. There is no evidence of binarity for this object. At [Fe/H]=-3.57, this star has one of the lowest metallicities currently observed, with 18 measured abundances of neutron-capture elements. The presence of Ba, La, and Ce abundances above the solar system r-process predictions suggests that there must have been a non-standard source of r-process elements operating at such low metallicities. One plausible explanation is that this enhancement originates from material ejected at unusually high velocities in a neutron star merger event. We also explore the possibility that the neutron-capture elements were produced during the evolution and explosion of a rotating massive star. In addition, based on comparisons with yields from zero-metallicity faint supernova, we speculate that RAVE-J1830-4555 was formed from a gas cloud pre-enriched by both progenitor types. From analysis based on Gaia DR2 measurements, we show that this star has orbital properties similar to the Galactic metal-weak thick-disk stellar population.
- ID:
- ivo://CDS.VizieR/J/ApJ/768/40
- Title:
- R-band and polarimetry of the blazar S5 0716+71
- Short Name:
- J/ApJ/768/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of optical (R band) photometric and polarimetric monitoring and Very Long Baseline Array (VLBA) imaging of the blazar S5 0716+714 along with Fermi {gamma}-ray data during a multi-waveband outburst in 2011 October. We analyze total and polarized intensity images of the blazar obtained with the VLBA at 43GHz during and after the outburst. Monotonic rotation of the linear polarization vector at a rate of >~50{deg} per night coincided with a sharp maximum in {gamma}-ray and optical flux. At the same time, within the uncertainties, a new superluminal knot appeared with an apparent speed of 21+/-2c. The general multi-frequency behavior of the outburst can be explained within the framework of a shock wave propagating along a helical path in the blazar's jet.
- ID:
- ivo://CDS.VizieR/J/ApJS/234/37
- Title:
- R-band K2 photometry of main-belt asteroids
- Short Name:
- J/ApJS/234/37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the K2 light curves of a large sample of untargeted main-belt asteroids (MBAs) detected with the Kepler Space Telescope. The asteroids were observed within the Uranus superstamp, a relatively large, continuous field with a low stellar background designed to cover the planet Uranus and its moons during Campaign 8 of the K2 mission. The superstamp offered the possibility of obtaining precise, uninterrupted light curves of a large number of MBAs and thus determining unambiguous rotation rates for them. We obtained photometry for 608 MBAs, and were able to determine or estimate rotation rates for 90 targets, of which 86 had no known values before. In an additional 16 targets we detected incomplete cycles and/or eclipse-like events. We found the median rotation rate to be significantly longer than that of the ground-based observations, indicating that the latter are biased toward shorter rotation rates. Our study highlights the need and benefits of further continuous photometry of asteroids.
- ID:
- ivo://CDS.VizieR/J/AJ/161/108
- Title:
- R-band light curve of Qatar-1
- Short Name:
- J/AJ/161/108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Motivated by the unsettled conclusion on whether there are any transit timing variations (TTVs) for the exoplanet Qatar-1b, 10 new transit light curves are presented and a TTV analysis with a baseline of 1400 epochs is performed. Because the linear model provides a good fit with a reduced chi-square of {chi}_red_^2^=2.59 and the false-alarm probabilities of the possible TTV frequencies are as large as 35%, our results are consistent with a null-TTV model. Nevertheless, a new ephemeris with a reference time of T0=2455647.63360{+/-}0.00008 (BJD) and a period of P=1.4200236{+/-}0.0000001day is obtained. In addition, the updated orbital semimajor axis and planetary radius in units of stellar radius are provided, and the lower limit of the modified stellar tidal quality factor is also determined.
- ID:
- ivo://CDS.VizieR/J/ApJ/756/52
- Title:
- R-band light curve of QSO J0158-4325 images
- Short Name:
- J/ApJ/756/52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present four new seasons of optical monitoring data and six epochs of X-ray photometry for the doubly imaged lensed quasar Q J0158-4325. The high-amplitude, short-period microlensing variability for which this system is known has historically precluded a time delay measurement by conventional methods. We attempt to circumvent this limitation by the application of a Monte Carlo microlensing analysis technique, but we are only able to prove that the delay must have the expected sign (image A leads image B). Despite our failure to robustly measure the time delay, we successfully model the microlensing at optical and X-ray wavelengths to find a half-light radius for soft X-ray emission log (r_1/2,X,soft_/cm)=14.3^+0.4^_-0.5_, an upper limit on the half-light radius for hard X-ray emission log (r_1/2,X,hard_/cm)<=14.6, and a refined estimate of the inclination-corrected scale radius of the optical R-band (rest frame 3100{AA}) continuum emission region of log (r_s_/cm)=15.6+/-0.3.
- ID:
- ivo://CDS.VizieR/J/ApJ/820/33
- Title:
- R-band light curves of type II supernovae
- Short Name:
- J/ApJ/820/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- During the first few days after explosion, Type II supernovae (SNe) are dominated by relatively simple physics. Theoretical predictions regarding early-time SN light curves in the ultraviolet (UV) and optical bands are thus quite robust. We present, for the first time, a sample of 57 R-band SN II light curves that are well-monitored during their rise, with >5 detections during the first 10 days after discovery, and a well-constrained time of explosion to within 1-3 days. We show that the energy per unit mass (E/M) can be deduced to roughly a factor of five by comparing early-time optical data to the 2011 model of Rabinak & Waxman, while the progenitor radius cannot be determined based on R-band data alone. We find that SN II explosion energies span a range of E/M=(0.2-20)x10^51^erg/(10M_{sun}), and have a mean energy per unit mass of <E/M>=0.85x10^51^erg/(10M_{sun}), corrected for Malmquist bias. Assuming a small spread in progenitor masses, this indicates a large intrinsic diversity in explosion energy. Moreover, E/M is positively correlated with the amount of ^56^Ni produced in the explosion, as predicted by some recent models of core-collapse SNe. We further present several empirical correlations. The peak magnitude is correlated with the decline rate ({Delta}m_15_), the decline rate is weakly correlated with the rise time, and the rise time is not significantly correlated with the peak magnitude. Faster declining SNe are more luminous and have longer rise times. This limits the possible power sources for such events.
