TY  - JOUR
A1  - Griggio, Massimo
A1  - Bedin, Luigi R.
A1  - Raddi, Roberto
A1  - Reindl, Nicole
A1  - Tomasella, Lina
A1  - Scalco, M.
A1  - Salaris, M.
A1  - Cassisi, S.
A1  - Ochner, P.
A1  - Ciroi, S.
A1  - Rosati, P.
A1  - Nardiello, Domenico
A1  - Anderson, J.
A1  - Libralato, Mattia
A1  - Bellini, A.
A1  - Vallenari, A.
A1  - Spina, L.
A1  - Pedani, M.
T1  - Astro-photometric study of M37 with Gaia and wide-field ugi-imaging
JF  - Monthly notices of the Royal Astronomical Society
N2  - We present an astrometric and photometric wide-field study of the Galactic open star cluster M37 (NGC 2099). The studied field was observed with ground-based images covering a region of about four square degrees in the Sloan-like filters ugi. We exploited the Gaia catalogue to calibrate the geometric distortion of the large field mosaics, developing software routines that can be also applied to other wide-field instruments. The data are used to identify the hottest white dwarf (WD) member candidates of M37. Thanks to the Gaia EDR3 exquisite astrometry we identified seven such WD candidates, one of which, besides being a high-probability astrometric member, is the putative central star of a planetary nebula. To our knowledge, this is a unique object in an open cluster, and we have obtained follow-up low-resolution spectra that are used for a qualitative characterization of this young WD. Finally, we publicly release a three-colour atlas and a catalogue of the sources in the field of view, which represents a complement of existing material.
KW  - catalogues
KW  - white dwarfs
KW  - open clusters and associations: individual:
KW  - M37 (NGC2099)
Y1  - 2022
U6  - https://doi.org/10.1093/mnras/stac1920
SN  - 0035-8711
SN  - 1365-2966
VL  - 515
IS  - 2
SP  - 1841
EP  - 1853
PB  - Oxford University Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Werner, Klaus
A1  - Reindl, Nicole
A1  - Dorsch, Matti
A1  - Geier, Stephan
A1  - Munari, Ulisse
A1  - Raddi, Roberto
T1  - Non-local thermodynamic equilibrium spectral analysis of five hot, hydrogen-deficient pre-white dwarfs
JF  - Astronomy and Astrophysics
N2  - Hot, compact, hydrogen-deficient pre-white dwarfs (pre-WDs) with effective temperatures of Teff > 70 000 K and a surface gravity of 5.0 < logg < 7.0 are rather rare objects despite recent and ongoing surveys. It is believed that they are the outcome of either single star evolution (late helium-shell flash or late helium-core flash) or binary star evolution (double WD merger). Their study is interesting because the surface elemental abundances reflect the physics of thermonuclear flashes and merger events. Spectroscopically they are divided in three different classes, namely PG1159, O(He), or He-sdO. We present a spectroscopic analysis of five such stars that turned out to have atmospheric parameters in the range Teff = 70 000-80 000 K and logg = 5.2-6.3. The three investigated He-sdOs have a relatively high hydrogen mass fraction (10%) that is unexplained by both single (He core flash) and binary evolution (He-WD merger) scenarios. The O(He) star JL 9 is probably a binary helium-WD merger, but its hydrogen content (6%) is also at odds with merger models. We found that RL 104 is the 'coolest' (Teff = 80 000 K) member of the PG1159 class in a pre-WD stage. Its optical spectrum is remarkable because it exhibits C※ IV lines involving Rydberg states with principal quantum numbers up to n = 22. Its rather low mass (0.48-0.02+0.03 M·) is difficult to reconcile with the common evolutionary scenario for PG1159 stars due to it being the outcome of a (very) late He-shell flash. The same mass-problem faces a merger model of a close He-sdO plus CO WD binary that predicts PG1159-like abundances. Perhaps RL 104 originates from a very late He-shell flash in a CO/He WD formed by a merger of two low-mass He-WDs.
KW  - stars: atmospheres
KW  - stars: abundances
KW  - stars: evolution
KW  - subdwarfs
KW  - white dwarfs
Y1  - 2022
U6  - https://doi.org/10.1051/0004-6361/202142397
SN  - 0004-6361
SN  - 1432-0746
VL  - 658
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Geier, Stephan
A1  - Raddi, Roberto
A1  - Fusillo, Nicola Pietro Gentile
A1  - Marsh, T. R.
T1  - The population of hot subdwarf stars studied with Gaia
BT  - II. The Gaia DR2 catalogue of hot subluminous stars
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Based on data from the ESA Gaia Data Release 2 (DR2) and several ground-based, multi-band photometry surveys we have 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 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 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.
KW  - subdwarfs
KW  - stars: horizontal-branch
KW  - catalogs
Y1  - 2019
U6  - https://doi.org/10.1051/0004-6361/201834236
SN  - 0004-6361
SN  - 1432-0746
VL  - 621
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Fusillo, Nicola Pietro Gentile
A1  - Tremblay, Pier-Emmanuel
A1  - Gänsicke, Boris T.
A1  - Manser, Christopher J.
A1  - Cunningham, Tim
A1  - Cukanovaite, Elena
A1  - Hollands, Mark
A1  - Marsh, Thomas
A1  - Raddi, Roberto
A1  - Jordan, Stefan
A1  - Toonen, Silvia
A1  - Geier, Stephan
A1  - Barstow, Martin
A1  - Cummings, Jeffrey D.
T1  - A Gaia Data Release 2 catalogue of white dwarfs and a comparison with SDSS
JF  - Monthly notices of the Royal Astronomical Society
N2  - We present a catalogue of white dwarf candidates selected from the second data release of Gaia (DR2). We used a sample of spectroscopically confirmed white dwarfs from the Sloan Digital Sky Survey (SDSS) to map the entire space spanned by these objects in the Gaia Hertzsprung–Russell diagram. We then defined a set of cuts in absolute magnitude, colour, and a number of Gaia quality flags to remove the majority of contaminating objects. Finally, we adopt a method analogous to the one presented in our earlier SDSS photometric catalogues to calculate a probability of being a white dwarf (PWD) for all Gaia sources that passed the initial selection. The final catalogue is composed of 486641 stars with calculated PWD from which it is possible to select a sample of ≃260000 high-confidence white dwarf candidates in the magnitude range 8 < G < 21. By comparing this catalogue with a sample of SDSS white dwarf candidates, we estimate an upper limit in completeness of 85 per cent for white dwarfs with G ≤ 20 mag and Teff >7000 K, at high Galactic latitudes (|b| > 20°). However, the completeness drops at low Galactic latitudes, and the magnitude limit of the catalogue varies significantly across the sky as a function of Gaia’s scanning law. We also provide the list of objects within our sample with available SDSS spectroscopy. We use this spectroscopic sample to characterize the observed structure of the white dwarf distribution in the H–R diagram.
KW  - catalogues
KW  - surveys
KW  - white dwarfs
Y1  - 2018
U6  - https://doi.org/10.1093/mnras/sty3016
SN  - 0035-8711
SN  - 1365-2966
VL  - 482
IS  - 4
SP  - 4570
EP  - 4591
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Raddi, Roberto
A1  - Hollands, M. A.
A1  - Koester, D.
A1  - Hermes, J. J.
A1  - Gansicke, B. T.
A1  - Heber, Ulrich
A1  - Shen, Ken J.
A1  - Townsley, D. M.
A1  - Pala, Anna Francesca
A1  - Reding, J. S.
A1  - Toloza, O. F.
A1  - Pelisoli, Ingrid Domingos
A1  - Geier, Stephan
A1  - Fusillo, Nicola Pietro Gentile
A1  - Munari, Ullisse
A1  - Strader, J.
T1  - Partly burnt runaway stellar remnants from peculiar thermonuclear supernovae
JF  - Monthly notices of the Royal Astronomical Society
N2  - We report the discovery of three stars that, along with the prototype LP 40-365, form a distinct class of chemically peculiar runaway stars that are the survivors of thermonuclear explosions. Spectroscopy of the four confirmed LP 40-365 stars finds ONe-dominated atmospheres enriched with remarkably similar amounts of nuclear ashes of partial O- and Si-burning. Kinematic evidence is consistent with ejection from a binary supernova progenitor; at least two stars have rest-frame velocities indicating they are unbound to the Galaxy. With masses and radii ranging between 0.20 and 0.28M(circle dot) and between 0.16 and 0.60 R-circle dot, respectively, we speculate these inflated white dwarfs are the partly burnt remnants of either peculiar Type Iax or electron-capture supernovae. Adopting supernova rates from the literature, we estimate that similar to 20 LP 40-365 stars brighter than 19 mag should be detectable within 2 kpc from the Sun at the end of the Gaia mission. We suggest that as they cool, these stars will evolve in their spectroscopic appearance, and eventually become peculiar O-rich white dwarfs. Finally, we stress that the discovery of new LP 40-365 stars will be useful to further constrain their evolution, supplying key boundary conditions to the modelling of explosion mechanisms, supernova rates, and nucleosynthetic yields of peculiar thermonuclear explosions.
KW  - stars: individual: LP 40-365
KW  - subdwarfs
KW  - supernovae: general
KW  - white dwarfs
KW  - Galaxy: kinematics and dynamics
Y1  - 2019
U6  - https://doi.org/10.1093/mnras/stz1618
SN  - 0035-8711
SN  - 1365-2966
VL  - 489
IS  - 2
SP  - 1489
EP  - 1508
PB  - Oxford Univ. Press
CY  - Oxford
ER  -