The population of hot subdwarf stars studied with Gaia II. The Gaia DR2 catalogue of hot subluminous stars

Based on data from the ESA Gaia Data Release 2 (DR2) and several ground-based, multi-band photometry surveys we compiled an all-sky catalogue of $39\,800$ hot subluminous star candidates selected in Gaia DR2 by means of colour, absolute magnitude and reduced proper motion cuts. We expect the majority of the candidates to be hot subdwarf stars of spectral type B and O, followed by blue horizontal branch stars of late B-type (HBB), hot post-AGB stars, and central stars of planetary nebulae. The contamination by cooler stars should be about $10\%$. The catalogue is magnitude limited to Gaia $G<19\,{\rm mag}$ and covers the whole sky. Except within the Galactic plane and LMC/SMC regions, we expect the catalogue to be almost complete up to about $1.5\,{\rm kpc}$. The main purpose of this catalogue is to serve as input target list for the large-scale photometric and spectroscopic surveys which are ongoing or scheduled to start in the coming years. In the long run, securing a statistically significant sample of spectroscopically confirmed hot subluminous stars is key to advance towards a more detailed understanding of the latest stages of stellar evolution for single and binary stars.Comment: 13 pages, A&A, accepte

The Field White Dwarf Mass Distribution

We revisit the properties and astrophysical implications of the field white dwarf mass distribution in preparation of Gaia applications. Our study is based on the two samples with the best established completeness and most precise atmospheric parameters, the volume-complete survey within 20 pc and the Sloan Digital Sky Survey (SDSS) magnitude-limited sample. We explore the modelling of the observed mass distributions with Monte Carlo simulations, but find that it is difficult to constrain independently the initial mass function (IMF), the initial-to-final-mass relation (IFMR), the stellar formation history (SFH), the variation of the Galactic disk vertical scale height as a function of stellar age, and binary evolution. Each of these input ingredients has a moderate effect on the predicted mass distributions, and we must also take into account biases owing to unidentified faint objects (20 pc sample), as well as unknown masses for magnetic white dwarfs and spectroscopic calibration issues (SDSS sample). Nevertheless, we find that fixed standard assumptions for the above parameters result in predicted mean masses that are in good qualitative agreement with the observed values. It suggests that derived masses for both studied samples are consistent with our current knowledge of stellar and Galactic evolution. Our simulations overpredict by 40-50% the number of massive white dwarfs (M > 0.75 Msun) for both surveys, although we can not exclude a Salpeter IMF when we account for all biases. Furthermore, we find no evidence of a population of double white dwarf mergers in the observed mass distributions.Comment: 15 pages, 16 figures, accepted for publication in MNRA

Do Homicide Perpetrators Have Higher Rates of Delayed-Suicide Than the Other Offenders? Data from a Sample of the Inmate Population in Italy

Homicide-suicide can be defined as homicide followed by the suicide of the perpetrator shortly afterward. In the so-called "homicide-delayed suicide", homicide and suicide occur but within a wide and not strictly defined timeframe. This study analyzes data concerning the suicide of 667 inmates in Italy between 2002 and 2015, considering homicide perpetrators compared to all offenders. The analyses revealed that inmates who had committed homicide were more likely to commit suicide (71% versus 45%; chi 2 = 10.952, p = 0.001) and the odds of suicide increase concerning 1.58 times among homicide perpetrators. The time-to-suicide interval after homicide ranges between 0 to 9.125 days (mean = 1.687,9; SD = 2.303,1). Moreover, the intimate-homicide offenders who committed suicide had a significantly shorter survival time after the offense than did the other non-intimate offenders who died by suicide (t test, t = -3.56, df = 90, p = 0.001). The link between homicide and higher suicide risk in homicide perpetrators should be highlighted because of all the homicide offenders passing through the criminal justice system. Superior knowledge about the path of homicide-delayed suicide will be of particular use to professionals in evaluating and treating homicide inmates. © 2022 by the authors

Towards an assessment of tree mortality and net annual increments in Italian forests. Which sustainability for the Italian forestry?

Sustainable forest management requires that fellings do not exceed increments in the medium term, once natural mortality is taken into account. Here we propose an assessment of the relevance of tree mortality in stands not regularly thinned, as prevailing in Italian forests. The amount of small-scale mortality losses is often neglected and cannot be directly estimated from available inventory data. From literature sources and using two alternative approaches, mortality losses could amount to 31.1-36.2% of gross annual increments. Fellings would therefore remove 57.7-62.6% of net annual increments of Italian forests, well above what often reported and not far away from the EU15 average. This new estimate confirms the overall sustainability of Italian forestry on a national level, but highlights the need for careful planning in the future use of forest biomass, a strategic renewable resource

When flux standards go wild: white dwarfs in the age of Kepler

White dwarf stars have been used as flux standards for decades, thanks to their staid simplicity. We have empirically tested their photometric stability by analyzing the light curves of 398 high-probability candidates and spectroscopically confirmed white dwarfs observed during the original Kepler mission and later with K2 Campaigns 0-8. We find that the vast majority (>97 per cent) of non-pulsating and apparently isolated white dwarfs are stable to better than 1 per cent in the Kepler bandpass on 1-hr to 10-d timescales, confirming that these stellar remnants are useful flux standards. From the cases that do exhibit significant variability, we caution that binarity, magnetism, and pulsations are three important attributes to rule out when establishing white dwarfs as flux standards, especially those hotter than 30,000 K.Comment: Accepted for publication in MNRAS; 7 pages, 4 figures, 2 table

A 3D extinction map of the northern Galactic plane based on IPHAS photometry

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. ©: 2014 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We present a 3D map of extinction in the northern Galactic plane derived using photometry from the INT/WFC Photometric Hα Survey of the northern Galactic plane. The map has fine angular (~10 arcmin) and distance (100 pc) sampling allied to a significant depth (≳5 kpc). We construct the map using a method based on a hierarchical Bayesian model described in a previous article by Sale. In addition to mean extinction, we also measure differential extinction, which arises from the fractal nature of the interstellar medium, and show that it will be the dominant source of uncertainty in estimates of extinction to some arbitrary position. The method applied also furnishes us with photometric estimates of the distance, extinction, effective temperature, surface gravity, and mass for ~38 million stars. Both the extinction map and the catalogue of stellar parameters are made publicly available via http://www.iphas.org/extinction.Peer reviewe

Role of xanthophyll cycle-mediated photoprotection in Arbutus unedo plants exposed to water stress during the Mediterranean summer

We analyzed the response of potted strawberry tree (Arbutus unedo L.) seedlings exposed to water stress by withholding water for 10 d (WS). Leaf water potential, net CO2 assimilation, and stomatal conductance decreased with increasing water deficit. A 30 % reduction of chlorophyll (Chl) content in the antenna complexes was observed in WS-plants. Simultaneously, a decline of photochemical efficiency (F-v/F-m) occurred as a result of an excess of solar radiation energy when carbon assimilation was limited by stomata closure due to soil water deficit. The non-photochemical quenching of Chl fluorescence (Phi(NPQ)) significantly increased, as well as the leaf contents of zeaxanthin (Z) and antheraxanthin (A) at the expense of violaxanthin during the WS-period. Elevated predawn contents of de-epoxidized xanthophyll cycle components were associated with a sustained lowering of predawn photosystem 2 efficiency; this suggested an engagement of Z+A in a state primed for energy dissipation. Thus, the ability of strawberry trees to maintain the functionality of the xanthophyll cycle during the Mediterranean summer is an efficient mechanism to prevent irreversible damages to the photosynthetic machinery through thermal energy dissipation in the antenna and the reduction in photochemical efficiency

SDSS J124043.01+671034.68 : the partially burned remnant of a low-mass white dwarf that underwent thermonuclear ignition?

The white dwarf SDSS J124043.01+671034.68 (SDSS J1240+6710) was previously found to have an oxygen-dominated atmosphere with significant traces of neon, magnesium, and silicon. A possible origin via a violent late thermal pulse or binary interactions have been suggested to explain this very unusual photospheric composition. We report the additional detection of carbon, sodium, and aluminium in far-ultraviolet and optical follow-up spectroscopy. No iron-group elements are detected, with tight upper limits on iron, cobalt and nickel, suggesting that the star underwent partial oxygen burning, but failed to ignite silicon burning. Modelling the spectral energy distribution and adopting the distance based on the Gaia parallax, we infer a low white dwarf mass, M(wd)=0.41+/-0.05Msun. The large space velocity of SDSS J1240+6710, computed from the Gaia proper motion and its radial velocity, is compatible with a Galactic rest-frame velocity of ~250km/s in the opposite direction with respect to the Galactic rotation, strongly supporting a binary origin of this star. We discuss the properties of SDSS J1240+6710 in the context of the recently identified survivors of thermonuclear supernovae, the D6 and LP 40-365 stars, and conclude that it is unlikely related to either of those two groups. We tentatively suggest that SDSS J1240+6710 is the partially burned remnant of a low-mass white dwarf that underwent a thermonuclear event.Comment: Accepted for publication in MNRA

Variable emission from a gaseous disc around a metal-polluted white dwarf

We present the discovery of strongly variable emission lines from a gaseous disc around the DA white dwarf SDSS J1617+1620, a star previously found to have an infrared excess indicative of a dusty debris disc formed by the tidal disruption of a rocky planetary body. Time series spectroscopy obtained during the period 2006–2014 has shown the appearance of strong double-peaked Ca II emission lines in 2008. The lines were weak, at best, during earlier observations, and monotonically faded through the remainder of our monitoring. Our observations represent unambiguous evidence for short-term variability in the debris environment of evolved planetary systems. Possible explanations for this extraordinary variability include the impact on to the dusty disc of either a single small rocky planetesimal, or of material from a highly eccentric debris tail. The increase in flux from the emission lines is sufficient that similar events could be detected in the broad-band photometry of ongoing and future large-area time domain surveys