14 research outputs found
Identification of Young Stellar Object candidates in the DR2 x AllWISE catalogue with machine learning methods
The second Data Release (DR2) contains astrometric and photometric
data for more than 1.6 billion objects with mean magnitude 20.7,
including many Young Stellar Objects (YSOs) in different evolutionary stages.
In order to explore the YSO population of the Milky Way, we combined the
DR2 database with WISE and Planck measurements and made an all-sky
probabilistic catalogue of YSOs using machine learning techniques, such as
Support Vector Machines, Random Forests, or Neural Networks. Our input
catalogue contains 103 million objects from the DR2xAllWISE cross-match table.
We classified each object into four main classes: YSOs, extragalactic objects,
main-sequence stars and evolved stars. At a 90% probability threshold we
identified 1,129,295 YSO candidates. To demonstrate the quality and potential
of our YSO catalogue, here we present two applications of it. (1) We explore
the 3D structure of the Orion A star forming complex and show that the spatial
distribution of the YSOs classified by our procedure is in agreement with
recent results from the literature. (2) We use our catalogue to classify
published Science Alerts. As measures the sources at multiple
epochs, it can efficiently discover transient events, including sudden
brightness changes of YSOs caused by dynamic processes of their circumstellar
disk. However, in many cases the physical nature of the published alert sources
are not known. A cross-check with our new catalogue shows that about 30% more
of the published alerts can most likely be attributed to YSO activity.
The catalogue can be also useful to identify YSOs among future alerts.Comment: 19 pages, 12 figures, 3 table
The large trans-Neptunian object 2002 TC302 from combined stellar occultation, photometry, and astrometry data
Context. Deriving physical properties of trans-Neptunian objects is important for the understanding of our Solar System. This requires observational efforts and the development of techniques suitable for these studies. Aims. Our aim is to characterize the large trans-Neptunian object (TNO) 2002 TC302. Methods. Stellar occultations offer unique opportunities to determine key physical properties of TNOs. On 28 January 2018, 2002 TC302 occulted a mv ~ 15.3 star with designation 593-005847 in the UCAC4 stellar catalog, corresponding to Gaia source 130957813463146112. Twelve positive occultation chords were obtained from Italy, France, Slovenia, and Switzerland. Also, four negative detections were obtained near the north and south limbs. This represents the best observed stellar occultation by a TNO other than Pluto in terms of the number of chords published thus far. From the 12 chords, an accurate elliptical fit to the instantaneous projection of the body can be obtained that is compatible with the near misses. Results. The resulting ellipse has major and minor axes of 543 ± 18 km and 460 ± 11 km, respectively, with a position angle of 3 ± 1 degrees for the minor axis. This information, combined with rotational light curves obtained with the 1.5 m telescope at Sierra Nevada Observatory and the 1.23 m telescope at Calar Alto observatory, allows us to derive possible three-dimensional shapes and density estimations for the body based on hydrostatic equilibrium assumptions. The effective diameter in equivalent area is around 84 km smaller than the radiometrically derived diameter using thermal data from Herschel and Spitzer Space Telescopes. This might indicate the existence of an unresolved satellite of up to ~300 km in diameter, which is required to account for all the thermal flux, although the occultation and thermal diameters are compatible within their error bars given the considerable uncertainty of the thermal results. The existence of a potential satellite also appears to be consistent with other ground-based data presented here. From the effective occultation diameter combined with absolute magnitude measurements we derive a geometric albedo of 0.147 ± 0.005, which would be somewhat smaller if 2002 TC302 has a satellite. The best occultation light curves do not show any signs of ring features or any signatures of a global atmosphere.Funding from Spanish projects AYA2014-56637-C2-1-P, AYA2017-89637-R, from FEDER, and Proyecto de Excelencia de la Junta de AndalucĂa 2012-FQM1776 is acknowledged. We would like to acknowledge financial support by the Spanish grant AYA-RTI2018-098657-JI00 âLEO-SBNAFâ (MCIU/AEI/FEDER, UE) and the financial support from the State Agency for Research of the Spanish MCIU through the âCenter of Excellence Severo Ochoaâ award for the Instituto de AstrofĂsica de AndalucĂa (SEV- 2017-0709). Part of the research received funding from the European Unionâs Horizon 2020 Research and Innovation Programme, under grant agreement no. 687378 and from the ERC programme under Grant Agreement no. 669416 Lucky Star. The following authors acknowledge the respective CNPq grants: FB-R 309578/2017-5; RV-M 304544/2017-5, 401903/2016-8; J.I.B.C. 308150/2016-3; MA 427700/2018-3, 310683/2017-3, 473002/2013-2. This study was financed in part by the Coordenação de Aperfeiaçoamento de Pessoal de NĂvel Superior - Brasil (CAPES) - Finance Code 001 and the National Institute of Science and Technology of the e-Universe project (INCT do e-Universo, CNPq grant 465376/2014-2). GBR acknowledges CAPES-FAPERJ/PAPDRJ grant E26/203.173/2016, MA FAPERJ grant E-26/111.488/2013 and ARGJr FAPESP grant 2018/11239-8. E.F.-V. acknowledges support from the 2017 Preeminent Postdoctoral Program (P3) at UCF. C.K., R.S., A.F-T., and G.M. have been supported by the K-125015 and GINOP-2.3.2-15-2016-00003 grants of the Hungarian National Research, Development and Innovation Office (NKFIH), Hungary. G.M. was also supported by the Hungarian National Research, Development and Innovation Office (NKFIH) grant PD-128 360. R.K. and T.P. were supported by the VEGA 2/0031/18 grant
SN 2016coi/ASASSN-16fp: an example of residual helium in a type Ic supernova?
The optical observations of Ic-4 supernova (SN) 2016coi/ASASSN-16fp, from âŒ2 to âŒ450 âd after explosion, are presented along with analysis of its physical properties. The SN shows the broad lines associated with SNe Ic-3/4 but with a key difference. The early spectra display a strong absorption feature at âŒ5400 Ă
which is not seen in other SNe Ic-3/4 at this epoch. This feature has been attributed to HeâI in the literature. Spectral modelling of the SN in the early photospheric phase suggests the presence of residual He in a C/O dominated shell. However, the behaviour of the HeâI lines is unusual when compared with He-rich SNe, showing relatively low velocities and weakening rather than strengthening over time. The SN is found to rise to peak âŒ16âd after core-collapse reaching a bolometric luminosity of LpâŒ3 Ă 1042 erg sâ1. Spectral models, including the nebular epoch, show that the SN ejected 2.5â4âMâ of material, with âŒ1.5âMâ below 5000 kmâsâ1, and with a kinetic energy of (4.5â7) Ă 1051âerg. The explosion synthesized âŒ0.14âMâ of 56Ni. There are significant uncertainties in E(B â V)host and the distance, however, which will affect Lp and MNi. SN 2016coi exploded in a host similar to the Large Magellanic Cloud (LMC) and away from star-forming regions. The properties of the SN and the host-galaxy suggest that the progenitor had MZAMS of 23â28âMâ and was stripped almost entirely down to its C/O core at explosion
The size, shape, density and ring of the dwarf planet Haumea from a stellar occultation
Haumeaâone of the four known trans-Neptunian dwarf planetsâis a very elongated and rapidly rotating body1, 2, 3. In contrast to other dwarf planets4, 5, 6, its size, shape, albedo and density are not well constrained. The Centaur Chariklo was the first body other than a giant planet known to have a ring system7, and the Centaur Chiron was later found to possess something similar to Charikloâs rings8, 9. Here we report observations from multiple Earth-based observatories of Haumea passing in front of a distant star (a multi-chord stellar occultation). Secondary events observed around the main body of Haumea are consistent with the presence of a ring with an opacity of 0.5, width of 70 kilometres and radius of about 2,287 kilometres. The ring is coplanar with both Haumeaâs equator and the orbit of its satellite Hiâiaka. The radius of the ring places it close to the 3:1 mean-motion resonance with Haumeaâs spin periodâthat is, Haumea rotates three times on its axis in the time that a ring particle completes one revolution. The occultation by the main body provides an instantaneous elliptical projected shape with axes of about 1,704 kilometres and 1,138 kilometres. Combined with rotational light curves, the occultation constrains the three-dimensional orientation of Haumea and its triaxial shape, which is inconsistent with a homogeneous body in hydrostatic equilibrium. Haumeaâs largest axis is at least 2,322 kilometres, larger than previously thought, implying an upper limit for its density of 1,885 kilograms per cubic metre and a geometric albedo of 0.51, both smaller than previous estimates1, 10, 11. In addition, this estimate of the density of Haumea is closer to that of Pluto than are previous estimates, in line with expectations. No global nitrogen- or methane-dominated atmosphere was detected.J.L.O. acknowledges funding from Spanish and Andalusian grants MINECO AYA-2014-56637-C2-1-P and J. A. 2012-FQM1776 as well as FEDER funds. Part of the research leading to these results received funding from the European Unionâs Horizon 2020 Research and Innovation Programme, under grant agreement no. 687378. B.S. acknowledges support from the French grants âBeyond Neptuneâ ANR-08-BLAN-0177 and âBeyond Neptune IIâ ANR-11-IS56-0002. Part of the research leading to these results has received funding from the European Research Council under the European Communityâs H2020 (2014-2020/ERC grant agreement no. 669416 âLucky Starâ). A.P. and R.S. have been supported by the grant LP2012-31 of the Hungarian Academy of Sciences. All of the Hungarian contributors acknowledge the partial support from K-125015 grant of the National Research, Development and Innovation Office (NKFIH). G.B.-R., F.B.-R., F.L.R., R.V.-M., J.I.B.C., M.A., A.R.G.-J. and B.E.M. acknowledge support from CAPES, CNPq and FAPERJ. J.C.G. acknowledges funding from AYA2015-63939-C2-2-P and from the Generalitat Valenciana PROMETEOII/2014/057. K.H. and P.P. were supported by the project RVO:67985815. The Astronomical Observatory of the Autonomous Region of the Aosta Valley acknowledges a Shoemaker NEO Grant 2013 from The Planetary Society. We acknowledge funds from a 2016 âResearch and Educationâ grant from Fondazione CRT. We also acknowledge the Slovakian project ITMS no. 26220120029
Identification of Young Stellar Object candidates in the Gaia DR2 x AllWISE catalogue with machine learning methods
The second Gaia Data Release (DR2) contains astrometric and photometric data for more than 1.6 billion objects with mean Gaia G magnitude <20.7, including many Young Stellar Objects (YSOs) in different evolutionary stages. In order to explore the YSO population of the Milky Way, we combined the Gaia DR2 data base with Wide-field Infrared Survey Explorer (WISE) and Planck measurements and made an all-sky probabilistic catalogue of YSOs using machine learning techniques, such as Support Vector Machines, Random Forests, or Neural Networks. Our input catalogue contains 103 million objects from the DR2xAllWISE cross- match table. We classified each object into four main classes: YSOs, extragalactic objects, main-sequence stars, and evolved stars. At a 90 per cent probability threshold, we identified 1 129 295 YSO candidates. To demonstrate the quality and potential of our YSO catalogue, here we present two applications of it. (1) We explore the 3D structure of the Orion A star-forming complex and show that the spatial distribution of the YSOs classified by our procedure is in agreement with recent results from the literature. (2) We use our catalogue to classify published Gaia Science Alerts. As Gaia measures the sources at multiple epochs, it can efficiently discover transient events, including sudden brightness changes of YSOs caused by dynamic processes of their circumstellar disc. However, in many cases the physical nature of the published alert sources are not known. A cross-check with our new catalogue shows that about 30 per cent more of the published Gaia alerts can most likely be attributed to YSO activity. The catalogue can be also useful to identify YSOs among future Gaia alerts
Small Bodies Near and Far (SBNAF): A benchmark study on physical and thermal properties of small bodies in the Solar System
The combination of visible and thermal data from the ground and astrophysics space missions is key to improving the scientific understanding of near-Earth, main-belt, trojans, centaurs, and trans-Neptunian objects. To get full information on a small sample of selected bodies we combine different methods and techniques: lightcurve inversion, stellar occultations, thermophysical modelling, radiometric methods, radar ranging and adaptive optics imaging. The SBNAF project will derive size, spin and shape, thermal inertia, surface roughness, and in some cases bulk densities and even internal structure and composition, for objects out to the most distant regions in the Solar System. The applications to objects with ground-truth information allows us to advance the techniques beyond the current state-of-the-art and to assess the limitations of each method. We present results from our project's first phase: the analysis of combined Herschel-KeplerK2 data and Herschel-occultation data for TNOs; synergy studies on large MBAs from combined high-quality visual and thermal data; establishment of well-known asteroids as celestial calibrators for far-infrared, sub-millimetre, and millimetre projects; first results on near-Earth asteroids properties from combined lightcurve, radar and thermal measurements, as well as the Hayabusa-2 mission target characterisation. We also introduce public web-services and tools for studies of small bodies in general. © 2017 COSPARThe research leading to these results has received funding from the European Union's Horizon 2020 Research and Innovation Programme, under Grant Agreement no. 687378