ABSTRACT Estimating a distance by inverting a parallax is only valid in the absence of noise. As most stars in the Gaia catalog will have non-negligible fractional parallax errors, we must treat ...distance estimation as a constrained inference problem. Here we investigate the performance of various priors for estimating distances, using a simulated Gaia catalog of one billion stars. We use three minimalist, isotropic priors, as well an anisotropic prior derived from the observability of stars in a Milky Way model. The two priors that assume a uniform distribution of stars-either in distance or in space density-give poor results: The root mean square fractional distance error, , grows far in excess of 100% once the fractional parallax error, , is larger than 0.1. A prior assuming an exponentially decreasing space density with increasing distance performs well once its single parameter-the scale length- has been set to an appropriate value: is roughly equal to for , yet does not increase further as increases up to to 1.0. The Milky Way prior performs well except toward the Galactic center, due to a mismatch with the (simulated) data. Such mismatches will be inevitable (and remain unknown) in real applications, and can produce large errors. We therefore suggest adopting the simpler exponentially decreasing space density prior, which is also less time-consuming to compute. Including Gaia photometry improves the distance estimation significantly for both the Milky Way and exponentially decreasing space density prior, yet doing so requires additional assumptions about the physical nature of stars.
ABSTRACT We infer distances and their asymmetric uncertainties for two million stars using the parallaxes published in the Gaia DR1 (GDR1) catalogue. We do this with two distance priors: A ...minimalist, isotropic prior assuming an exponentially decreasing space density with increasing distance, and an anisotropic prior derived from the observability of stars in a Milky Way model. We validate our results by comparing our distance estimates for 105 Cepheids which have more precise, independently estimated distances. For this sample we find that the Milky Way prior performs better (the rms of the scaled residuals is 0.40) than the exponentially decreasing space density prior (rms is 0.57), although for distances beyond 2 kpc the Milky Way prior performs worse, with a bias in the scaled residuals of −0.36 (versus −0.07 for the exponentially decreasing space density prior). We do not attempt to include the photometric data in GDR1 due to the lack of reliable color information. Our distance catalog is available at http://www.mpia.de/homes/calj/tgas_distances/main.html as well as at CDS. This should only be used to give individual distances. Combining data or testing models should be done with the original parallaxes, and attention paid to correlated and systematic uncertainties.
Abstract
We report individual dynamical masses for the brown dwarfs
ε
Indi B and C, which have spectral types of T1.5 and T6, respectively, measured from astrometric orbit mapping. Our measurements ...are based on a joint analysis of astrometric data from the Carnegie Astrometric Planet Search and the Cerro Tololo Inter-American Observatory Parallax Investigation, as well as archival high-resolution imaging, and use a Markov chain Monte Carlo method. We find dynamical masses of 75.0 ± 0.82
M
Jup
for the T1.5 B component and 70.1 ± 0.68
M
Jup
for the T6 C component. These masses are surprisingly high for such cool objects and challenge our understanding of substellar structure and evolution. We discuss several evolutionary scenarios proposed in the literature and find that while none of them can provide conclusive explanations for the high substellar masses, evolutionary models incorporating lower atmospheric opacities come closer to approximating our results. We discuss the details of our astrometric model, its algorithm implementation, and how we determine parameter values via Markov chain Monte Carlo Bayesian inference.
Transit photometry of the M8V dwarf star TRAPPIST-1 (2MASS J23062928-0502285) has revealed the presence of at least seven planets with masses and radii similar to that of Earth, orbiting at distances ...that might allow liquid water to be present on their surfaces. We have been following TRAPPIST-1 since 2011 with the CAPSCam astrometric camera on the 2.5 m du Pont telescope at the Las Campanas Observatory in Chile. In 2016, we noted that TRAPPIST-1 lies slightly farther away than previously thought, at 12.49 pc, rather than 12.1 pc. Here, we examine 15 epochs of CAPSCam observations of TRAPPIST-1, spanning the five years from 2011 to 2016, and obtain a revised trigonometric distance of 12.56 0.12 pc. The astrometric data analysis pipeline shows no evidence for a long-period astrometric wobble of TRAPPIST-1. After proper motion and parallax are removed, residuals at the level of 1.3 mas remain. The amplitude of these residuals constrains the masses of any long-period gas giant planets in the TRAPPIST-1 system: no planet more massive than ∼4.6 MJup orbits with a 1 year period, and no planet more massive than ∼1.6 MJup orbits with a 5 year period. Further refinement of the CAPSCam data analysis pipeline, combined with continued CAPSCam observations, should either detect any long-period planets, or put an even tighter constraint on these mass upper limits.
This is a preliminary study to examine the prospect of detecting Tetraelectronvolt 1012 eV (TeV) photons from γ-ray bursts (GRB) using km-sized neutrino telescopes, specifically for the ANTARES ...neutrino telescope. Although optimized to detect upgoing neutrino-induced muons, neutrino telescopes nevertheless have a potential to detect high-energy photons by detecting downgoing muons from the electromagnetic cascade induced by the interaction of TeV photons with the Earth's atmosphere. The photon energy spectrum of a GRB is modelled by a simple power law and is normalized by simple energy considerations. Taking into account the absorption of TeV photons by cosmic infrared backgrounds, an optical depth table calculated from a model by Finke, Razzaque & Dermer is used and the arriving number of photons on top of the Earth atmosphere is determined. Muon production in the atmosphere is determined by considering two main channels of muon production: pion photoproduction and direct muon pair production. The muon energy loss during their traverse from the surface to the bottom of the sea is determined using the standard muon energy loss formula. Assuming different detector sizes, the number of detectable muons from single GRB events located at different redshifts and zenith distances is determined. The background is calculated assuming it consists primarily of cosmic ray induced downgoing muons. The detection significance is calculated and it can be concluded that to obtain at least 3σ detection significance, a typical GRB has to be located at redshift z≲ 0.07 if the detector's muon effective area is A
μ
eff∼ 10−2 km2, or redshift z≲ 0.15, if the muon effective area is A
μ
eff∼ 1 km2.
ABSTRACT This is a preliminary study to examine the prospect of detecting Tetraelectronvolt 1012 eV (TeV) photons from γ-ray bursts (GRB) using km-sized neutrino telescopes, specifically for the ...ANTARES neutrino telescope. Although optimized to detect upgoing neutrino-induced muons, neutrino telescopes nevertheless have a potential to detect high-energy photons by detecting downgoing muons from the electromagnetic cascade induced by the interaction of TeV photons with the Earth's atmosphere. The photon energy spectrum of a GRB is modelled by a simple power law and is normalized by simple energy considerations. Taking into account the absorption of TeV photons by cosmic infrared backgrounds, an optical depth table calculated from a model by Finke, Razzaque & Dermer is used and the arriving number of photons on top of the Earth atmosphere is determined. Muon production in the atmosphere is determined by considering two main channels of muon production: pion photoproduction and direct muon pair production. The muon energy loss during their traverse from the surface to the bottom of the sea is determined using the standard muon energy loss formula. Assuming different detector sizes, the number of detectable muons from single GRB events located at different redshifts and zenith distances is determined. The background is calculated assuming it consists primarily of cosmic ray induced downgoing muons. The detection significance is calculated and it can be concluded that to obtain at least 3σ detection significance, a typical GRB has to be located at redshift z 0.07 if the detector's muon effective area is A μeff 10-2km2, or redshift z 0.15, if the muon effective area is A μeff 1km2. PUBLICATION ABSTRACT
The detection principle of ANTARES and its sensitivity to GRB neutrinos will be discussed. Latest analysis of ANTARES data in coincidence with GRB direction and time of occurence will also be ...presented, as well as the prospects of neutrino detection with KM3NeT, the km3 neutrino telescope that will succeed ANTARES.
We report individual dynamical masses for the brown dwarfs Indi B and C, which have spectral types of T1.5 and T6, respectively, measured from astrometric orbit mapping. Our measurements are based on ...a joint analysis of astrometric data from the Carnegie Astrometric Planet Search and the Cerro Tololo Inter-American Observatory Parallax Investigation, as well as archival high-resolution imaging, and use a Markov chain Monte Carlo method. We find dynamical masses of 75.0 0.82 MJup for the T1.5 B component and 70.1 0.68 MJup for the T6 C component. These masses are surprisingly high for such cool objects and challenge our understanding of substellar structure and evolution. We discuss several evolutionary scenarios proposed in the literature and find that while none of them can provide conclusive explanations for the high substellar masses, evolutionary models incorporating lower atmospheric opacities come closer to approximating our results. We discuss the details of our astrometric model, its algorithm implementation, and how we determine parameter values via Markov chain Monte Carlo Bayesian inference.
The deep ocean is the largest and least known ecosystem on Earth. It hosts numerous pelagic organisms, most of which are able to emit light. Here we present a unique data set consisting of a 2.5-year ...long record of light emission by deep-sea pelagic organisms, measured from December 2007 to June 2010 at the ANTARES underwater neutrino telescope in the deep NW Mediterranean Sea, jointly with synchronous hydrological records. This is the longest continuous time-series of deep-sea bioluminescence ever recorded. Our record reveals several weeks long, seasonal bioluminescence blooms with light intensity up to two orders of magnitude higher than background values, which correlate to changes in the properties of deep waters. Such changes are triggered by the winter cooling and evaporation experienced by the upper ocean layer in the Gulf of Lion that leads to the formation and subsequent sinking of dense water through a process known as "open-sea convection". It episodically renews the deep water of the study area and conveys fresh organic matter that fuels the deep ecosystems. Luminous bacteria most likely are the main contributors to the observed deep-sea bioluminescence blooms. Our observations demonstrate a consistent and rapid connection between deep open-sea convection and bathypelagic biological activity, as expressed by bioluminescence. In a setting where dense water formation events are likely to decline under global warming scenarios enhancing ocean stratification, in situ observatories become essential as environmental sentinels for the monitoring and understanding of deep-sea ecosystem shifts.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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