scholarly journals White dwarfs with planetary remnants in the era of Gaia I: six emission line systems

2021 ◽  
Author(s):  
N P Gentile Fusillo ◽  
C J Manser ◽  
Boris T Gänsicke ◽  
O Toloza ◽  
D Koester ◽  
...  
Keyword(s):  
White Dwarfs ◽  
Emission Lines ◽  
Evolutionary Stage ◽  
Infrared Excess ◽  
The Standard Model ◽  
First Results ◽  
Five Elements ◽  
Case Basis ◽  
Gaia Dr2 ◽  
Shed Light

Abstract White dwarfs with emission lines from gaseous debris discs are among the rarest examples of planetary remnant hosts, but at the same time they are key objects for studying the final evolutionary stage of planetary systems. Making use of the large number of white dwarfs identified in Gaia DR2, we are conducting a survey of planetary remnants and here we present the first results of our search: six white dwarfs with gaseous debris discs. This first publication focuses on the main observational properties of these objects and highlights their most unique features. Three systems in particular stand out: WD J084602.47+570328.64 displays an exceptionally strong infrared excess which defies the standard model of a geometrically-thin, optically-thick dusty debris disc; WD J213350.72+242805.93 is the hottest gaseous debris disc host known with ${T_{\rm{eff}}}=29\, 282$ K; and WD J052914.32–340108.11, in which we identify a record number of 51 emission lines from five elements. These discoveries shed light on the underlying diversity in gaseous debris disc systems and bring the total number of these objects to 21. With these numbers we can now start looking at the properties of these systems as a class of objects rather than on a case-by-case basis.

scholarly journals Three Hypervelocity White Dwarfs in Gaia DR2: Evidence for Dynamically Driven Double-degenerate Double-detonation Type Ia Supernovae

2018 ◽  
Vol 865 (1) ◽  
pp. 15 ◽  
Author(s):  
Ken J. Shen ◽  
Douglas Boubert ◽  
Boris T. Gänsicke ◽  
Saurabh W. Jha ◽  
Jennifer E. Andrews ◽  
...  
Keyword(s):  
White Dwarfs ◽  
Type Ia Supernovae ◽  
Type Ia ◽  
Ia Supernovae ◽  
Gaia Dr2

scholarly journals Emission lines from tidally disrupted white dwarfs and other evolved stars

2012 ◽  
Vol 39 ◽  
pp. 01005 ◽  
Author(s):  
D. Clausen ◽  
M. Eracleous ◽  
S. Sigurdsson ◽  
J.A. Irwin
Keyword(s):  
White Dwarfs ◽  
Emission Lines ◽  
Evolved Stars

Towards Human-Centered AI: Psychological concepts as foundation for empirical XAI research

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Katharina Weitz
Keyword(s):  
Machine Learning ◽  
Mental Models ◽  
Empirical Studies ◽  
End Users ◽  
User Needs ◽  
Specific Task ◽  
Explainable Ai ◽  
First Results ◽  
Shed Light ◽  
Psychological Concepts

Abstract Human-Centered AI is a widely requested goal for AI applications. To reach this is explainable AI promises to help humans to understand the inner workings and decisions of AI systems. While different XAI techniques have been developed to shed light on AI systems, it is still unclear how end-users with no experience in machine learning perceive these. Psychological concepts like trust, mental models, and self-efficacy can serve as instruments to evaluate XAI approaches in empirical studies with end-users. First results in applications for education, healthcare, and industry suggest that one XAI does not fit all. Instead, the design of XAI has to consider user needs, personal background, and the specific task of the AI system.

scholarly journals The frequency of gaseous debris discs around white dwarfs

2020 ◽  
Vol 493 (2) ◽  
pp. 2127-2139 ◽  
Author(s):  
Christopher J Manser ◽  
Boris T Gänsicke ◽  
Nicola Pietro Gentile Fusillo ◽  
Richard Ashley ◽  
Elmé Breedt ◽  
...  
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Signal To Noise Ratio ◽  
Infrared Emission ◽  
Sloan Digital Sky Survey ◽  
Emission Lines ◽  
Occurrence Rate ◽  
Limited Sample ◽  
Sky Survey ◽  
Gaseous Disc

ABSTRACT A total of 1–3 per cent of white dwarfs are orbited by planetary dusty debris detectable as infrared emission in excess above the white dwarf flux. In a rare subset of these systems, a gaseous disc component is also detected via emission lines of the Ca ii 8600 Å triplet, broadened by the Keplerian velocity of the disc. We present the first statistical study of the fraction of debris discs containing detectable amounts of gas in emission at white dwarfs within a magnitude and signal-to-noise ratio limited sample. We select 7705 single white dwarfs spectroscopically observed by the Sloan Digital Sky Survey (SDSS) and Gaia with magnitudes g ≤ 19. We identify five gaseous disc hosts, all of which have been previously discovered. We calculate the occurrence rate of a white dwarf hosting a debris disc detectable via Ca ii emission lines as $0.067\, \pm \, ^{0.042}_{0.025}$ per cent. This corresponds to an occurrence rate for a dusty debris disc to have an observable gaseous component in emission as 4 ± $_{2}^{4}$ per cent. Given that variability is a common feature of the emission profiles of gaseous debris discs, and the recent detection of a planetesimal orbiting within the disc of SDSS J122859.93+104032.9, we propose that gaseous components are tracers for the presence of planetesimals embedded in the discs and outline a qualitative model. We also present spectroscopy of the Ca ii triplet 8600 Å region for 20 white dwarfs hosting dusty debris discs in an attempt to identify gaseous emission. We do not detect any gaseous components in these 20 systems, consistent with the occurrence rate that we calculated.

scholarly journals Variability of NGC 3783: First Results from an Intensive Ground-Based Monitoring Campaign

1994 ◽  
Vol 159 ◽  
pp. 407-407
Author(s):  
Giovanna M. Stirpe
Keyword(s):  
Emission Lines ◽  
Intensive Monitoring ◽  
Monitoring Campaign ◽  
Broad Emission ◽  
Photometric Observations ◽  
First Results ◽  
The Continuum

The International AGN Watch collaboration undertook an intensive monitoring campaign of the bright Seyfert 1 galaxy NGC 3783 between December 1991 and August 1992, in order to study the variations of the continuum and broad emission lines. Spectroscopic and photometric observations took place at several ground-based observatories and formed the optical/IR counterpart to the UV observations conducted with the IUE (Reichert et al. 1993).

The completeness of Gaia-selected samples of white dwarfs

2019 ◽  
Vol 15 (S357) ◽  
pp. 170-174
Author(s):  
Terry D. Oswalt ◽  
Jay B. Holberg ◽  
Edward M. Sion
Keyword(s):  
White Dwarf ◽  
Proper Motion ◽  
White Dwarfs ◽  
Color Index ◽  
Apparent Magnitude ◽  
Order Of Magnitude ◽  
Gaia Dr2 ◽  
Photometric Color

AbstractThe Gaia DR2 has dramatically increased the ability to detect faint nearby white dwarfs. The census of the local white dwarf population has recently been extended from 25 pc to 50 pc, effectively increasing the sample by roughly an order of magnitude. Here we examine the completeness of this new sample as a function of variables such as apparent magnitude, distance, proper motion, photometric color index, unresolved components, etc.

scholarly journals STUDY OF THE ELECTROMAGNETIC TRANSITIONS J/ψ → P l+l- AND PROBE DARK PHOTON

2012 ◽  
Vol 27 (38) ◽  
pp. 1250223 ◽  
Author(s):  
JINLIN FU ◽  
HAI-BO LI ◽  
XIAOSHUAI QIN ◽  
MAO-ZHI YANG
Keyword(s):  
Form Factor ◽  
Internal Conversion ◽  
Massive Particle ◽  
Lepton Pairs ◽  
Data Set ◽  
Decay Modes ◽  
Electromagnetic Structure ◽  
Dark Photon ◽  
The Standard Model ◽  
Shed Light

We study the electromagnetic Dalitz decay modes of J/ψ → P l+l- (P = π0, η or η′). In these decays, the lepton pairs are formed by internal conversion of an intermediate virtual photon with invariant mass ml+l-. Study of the effective-mass spectrum of the l+l- will shed light on the dynamic transition form factor [Formula: see text], which characterizes the electromagnetic structure arising at the vertex of the transition J/ψ to pseudoscalars. We also discuss the direct productions of a GeV scale vector U boson in these processes J/ψ → PU (U → l+l-). It is responsible for mediating a new U(1)d interaction, as recently exploited in the context of weakly interacting massive particle dark matter. In this paper, we firstly use the usual pole approximation for the form factor to estimate the decay rate of J/ψ → P l+l- in the Standard Model. Then the reach of searching for the dark photon is estimated. We suggest that these Dalitz decays can be used to search for the light U boson in the BESIII experiment with a huge J/ψ data set.

scholarly journals Spectroscopic Investigations of Luminous Emission-Line Objects

1975 ◽  
Vol 67 ◽  
pp. 297-298
Author(s):  
Angelo Cassatella ◽  
Roberto Nesci ◽  
Roberto Viotti
Keyword(s):  
Mass Loss ◽  
Emission Line ◽  
Physical Characteristics ◽  
Emission Lines ◽  
Expansion Velocity ◽  
Evolutionary Stage ◽  
High Luminosity ◽  
Spectroscopic Investigations ◽  
Differential Expansion ◽  
Parent Star

Emission lines are frequently observed in the spectra of the high luminosity stars, indicating the presence of extended atmospheric envelopes. We are investigating the physical characteristics (differential expansion velocity, density, extension, mass loss) and the origin of these envelopes in relation to the high luminosity of the parent star, and its evolutionary stage. Some results are presented concerning Eta Car, S Dor, HD 34664, P Cyg, AG and HR Car, and two WR stars.

scholarly journals Abundances of Wolf-Rayet stars as metallicity tracers

1999 ◽  
Vol 193 ◽  
pp. 252-253
Author(s):  
Maria Auxiliadora Delgado Machado
Keyword(s):  
Standard Model ◽  
Numerical Code ◽  
The Standard Model ◽  
First Results

We present here the first results of a grid of helium-carbon-oxygen models for Wolf-Rayet stars of the carbon sequence (WC). The models were calculated with a numerical code that assumes the basic considerations of the standard model.

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