Double white dwarf binaries with merger timescales smaller than the Hubble time and
with a total mass near the Chandrasekhar limit (i.e. classical Chandrasekhar population) or with high-mass ...primaries (i.e. sub-Chandrasekhar population) are potential
supernova type Ia (SNIa) progenitors. However, we have not yet unambiguously confirmed the existence of these objects observationally, a fact that has been often used to
criticise the relevance of double white dwarfs for producing SNIa. We analyse whether
this lack of detections is due to observational effects. To that end we simulate the
double white dwarf binary population in the Galaxy and obtain synthetic spectra for
the SNIa progenitors. We demonstrate that their identification, based on the detection of Ha double-lined profiles arising from the two white dwarfs in the synthetic
spectra, is extremely challenging due to their intrinsic faintness. This translates into
an observational probability of finding double white dwarf SNIa progenitors in the
Galaxy of (2.1 ± 1.0) × 10-5 and (0.8 ± 0.4) × 10-5
for the classical Chandrasekhar and
the sub-Chandrasekhar progenitor populations, respectively. Eclipsing double white
dwarf SNIa progenitors are found to suffer from the same observational effect. The
next generation of large-aperture telescopes are expected to help in increasing the
probability for detection by ~1 order of magnitude. However, it is only with forthcoming observations such as those provided by LISA that we expect to unambiguously
confirm or disprove the existence of double white dwarf SNIa progenitors and to test
their importance for producing SNIa.
Peer Reviewed
The scatter of the M dwarf mass–radius relationship Parsons, S G; Gänsicke, B T; Marsh, T R ...
Monthly notices of the Royal Astronomical Society,
11/2018, Letnik:
481, Številka:
1
Journal Article, Publication
Recenzirano
Odprti dostop
M dwarfs are prime targets in the hunt for habitable worlds around other stars. This
is due to their abundance as well as their small radii and low masses and tempera-
tures, which facilitate the ...detection of temperate, rocky planets in orbit around them.
However, the fundamental properties of M dwarfs are difficult to constrain, often lim-
iting our ability to characterise the planets they host. Here we test several theoretical
relationships for M dwarfs by measuring 23 high precision, model-independent masses
and radii for M dwarfs in binaries with white dwarfs. We find a large scatter in the
radii of these low-mass stars, with 25 per cent having radii consistent with theoret-
ical models while the rest are up to 12 per cent over-inflated. This scatter is seen
in both partially- and fully-convective M dwarfs. No clear trend is seen between the
over-inflation and age or metallicity, but there are indications that the radii of slowly
rotating M dwarfs are more consistent with predictions, albeit with a similar amount of
scatter in the measurements compared to more rapidly rotating M dwarfs. The sample
of M dwarfs in close binaries with white dwarfs appears indistinguishable from other
M dwarf samples, implying that common envelope evolution has a negligible impact on
their structure. We conclude that theoretical and empirical mass-radius relationships
lack the precision and accuracy required to measure the fundamental parameters of
M dwarfs well enough to determine the internal structure and bulk composition of the
planets they host.
Peer Reviewed
We present a catalogue of 73¿221 white dwarf candidates extracted from the astrometric and photometric data of the recently published Gaia-DR2 catalogue. White dwarfs were selected from the Gaia ...Hertzsprung–Russell diagram with the aid of the most updated population synthesis simulator. Our analysis shows that Gaia has virtually identified all white dwarfs within 100¿pc from the Sun. Hence, our sub-population of 8555 white dwarfs within this distance limit and the colour range considered, -0.52<(GBP-GRP)<0.80¿, is the largest and most complete volume-limited sample of such objects to date. From this sub-sample, we identified 8343 CO-core and 212 ONe-core white dwarf candidates and derived a white dwarf space density of 4.9±0.4×10-3pc-3¿. A bifurcation in the Hertzsprung–Russell diagram for these sources, which our models do not predict, is clearly visible. We used the Virtual Observatory SED Analyzer tool to derive effective temperatures and luminosities for our sources by fitting their spectral energy distributions, that we built from the ultraviolet to the near-infrared using publicly available photometry through the Virtual Observatory. From these parameters, we derived the white dwarf radii. Interpolating the radii and effective temperatures in hydrogen-rich white dwarf cooling sequences, we derived the surface gravities and masses. The Gaia 100¿pc white dwarf population is clearly dominated by cool (~8000¿K) objects and reveals a significant population of massive (¿M~0.8M¿¿) white dwarfs, of which no more than ~30--40 per cent can be attributed to hydrogen-deficient atmospheres, and whose origin remains uncertain.
Peer Reviewed
ABSTRACT
The Gaia mission has provided an unprecedented wealth of information about the white dwarf population of our Galaxy. In particular, our studies show that the sample up to 100 pc from the Sun ...can be considered as practically complete. This fact allows us to estimate a precise fraction of double-degenerate (1.18 ± 0.10 per cent) and white dwarf plus main-sequence stars (6.31 ± 0.23 per cent) among all white dwarfs through comoving pairs identification. With the aid of a detailed population synthesis code, we are able to reproduce synthetic white dwarf populations with nearly identical fractions as the observed ones, thus obtaining valuable information about the binary fraction, fb, initial mass ratio distribution, n(q), and initial separation distribution, f(a), among other parameters. Our best-fitting model is achieved within a 1σ confidence level for f(a) ∝ a−1, $n(q)\propto q^{n_q}$, with $n_q=-1.13^{+0.12}_{-0.10}$ and fb = 0.32 ± 0.02. The fraction of white dwarf mergers generated by this model is $9\sim 16{{\ \rm per\ cent}}$, depending on the common-envelope treatment. As sub-products of our modelling, we find that around $1\sim 3{{\ \rm per\ cent}}$ of the white dwarf population are unresolved double-degenerates and that only ${\sim}1{{\ \rm per\ cent}}$ of all white dwarfs contain a He-core. Finally, only a mild kick during white dwarf formation seems to be necessary for fitting the observed sky separation of double-degenerate systems.
ABSTRACT
We use the data provided by the Gaia Early Data Release 3 to search for a highly complete volume-limited sample of unresolved binaries consisting of a white dwarf and a main-sequence ...companion (i.e. WDMS binaries) within 100 pc. We select 112 objects based on their location within the Hertzsprung–Russell diagram, of which 97 are new identifications. We fit their spectral energy distributions (SED) with a two-body fitting algorithm implemented in VOSA (Virtual Observatory SED Analyser) to derive the effective temperatures, luminosities, and radii (hence surface gravities and masses) of both components. The stellar parameters are compared to those from the currently largest catalogue of close WDMS binaries, from the Sloan Digital Sky Survey (SDSS). We find important differences between the properties of the Gaia and SDSS samples. In particular, the Gaia sample contains WDMS binaries with considerably cooler white dwarfs and main-sequence companions (some expected to be brown dwarfs). The Gaia sample also shows an important population of systems consisting of cool and extremely low-mass white dwarfs, not present in the SDSS sample. Finally, using a Monte Carlo population synthesis code, we find that the volume-limited sample of systems identified here seems to be highly complete (≃ 80 ± 9 per cent); however, it only represents ≃9 per cent of the total underlying population. The missing ≃91 per cent includes systems in which the main-sequence companions entirely dominate the SEDs. We also estimate an upper limit to the total space density of close WDMS binaries of ≃ (3.7 ± 1.9) × 10−4 pc−3.
ABSTRACT
Gaia-DR2 has provided an unprecedented number of white dwarf candidates of our Galaxy. In particular, it is estimated that Gaia-DR2 has observed nearly 400 000 of these objects and close to ...18 000 up to 100 pc from the Sun. This large quantity of data requires a thorough analysis in order to uncover their main Galactic population properties, in particular the thin and thick disc and halo components. Taking advantage of recent developments in artificial intelligence techniques, we make use of a detailed Random Forest algorithm to analyse an 8D space (equatorial coordinates, parallax, proper motion components, and photometric magnitudes) of accurate data provided by Gaia-DR2 within 100 pc from the Sun. With the aid of a thorough and robust population synthesis code, we simulated the different components of the Galactic white dwarf population to optimize the information extracted from the algorithm for disentangling the different population components. The algorithm is first tested in a known simulated sample achieving an accuracy of 85.3 per cent. Our methodology is thoroughly compared to standard methods based on kinematic criteria demonstrating that our algorithm substantially improves previous approaches. Once trained, the algorithm is then applied to the Gaia-DR2 100 pc white dwarf sample, identifying 12 227 thin disc, 1410 thick disc, and 95 halo white dwarf candidates, which represent a proportion of 74:25:1, respectively. Hence, the numerical spatial densities are $(3.6\pm 0.4)\times 10^{-3}\, {\rm pc^{-3}}$, $(1.2\pm 0.4)\times 10^{-3}\, {\rm pc^{-3}}$, and $(4.8\pm 0.4)\times 10^{-5}\, {\rm pc^{-3}}$ for the thin disc, thick disc, and halo components, respectively. The populations thus obtained represent the most complete and volume-limited samples to date of the different components of the Galactic white dwarf population.
Abstract
We present high-precision, model-independent, mass and radius measurements for 16 white dwarfs in detached eclipsing binaries and combine these with previously published data to test the ...theoretical white dwarf mass–radius relationship. We reach a mean precision of 2.4 per cent in mass and 2.7 per cent in radius, with our best measurements reaching a precision of 0.3 per cent in mass and 0.5 per cent in radius. We find excellent agreement between the measured and predicted radii across a wide range of masses and temperatures. We also find the radii of all white dwarfs with masses less than 0.48 M⊙ to be fully consistent with helium core models, but they are on average 9 per cent larger than those of carbon–oxygen core models. In contrast, white dwarfs with masses larger than 0.52 M⊙ all have radii consistent with carbon–oxygen core models. Moreover, we find that all but one of the white dwarfs in our sample have radii consistent with possessing thick surface hydrogen envelopes (10−5 ≥ M
H/M
WD ≥ 10−4), implying that the surface hydrogen layers of these white dwarfs are not obviously affected by common envelope evolution.
Abstract
We present a Monte Carlo population synthesis study of white dwarf–main sequence (WD+MS) binaries in the Galactic disc aimed at reproducing the ensemble properties of the entire population ...observed by the Sloan Digital Sky Survey (SDSS) Data Release 12. Our simulations take into account all known observational biases and use the most up-to-date stellar evolutionary models. This allows us to perform a sound comparison between the simulations and the observational data. We find that the properties of the simulated and observed parameter distributions agree best when assuming low values of the common envelope efficiency (0.2–0.3), a result that is in agreement with previous findings obtained by observational and population synthesis studies of close SDSS WD+MS binaries. We also show that all synthetic populations that result from adopting an initial mass ratio distribution with a positive slope are excluded by observations. Finally, we confirm that the properties of the simulated WD+MS binary populations are nearly independent of the age adopted for the thin disc, on the contribution of WD+MS binaries from the thick disc (0–17 per cent of the total population) and on the assumed fraction of the internal energy that is used to eject the envelope during the common envelope phase (0.1–0.5).
ABSTRACT
The third data release of Gaia has provided low-resolution spectra for ∼100 000 white dwarfs (WDs) that, together with the excellent photometry and astrometry, represent an unrivalled ...benchmark for the study of this population. In this work, we first built a highly complete volume-limited sample consisting in 12 718 WDs within 100 pc from the Sun. The use of Virtual Observatory Spectral energy distribution Analyzer tool allowed us to perform an automated fitting of their spectral energy distributions to different atmospheric models. In particular, the use of spectrally derived Javalambre-Physics of the Accelerating Universe Astrophysical Survey photometry from Gaia spectra led to the classification of DA and non-DA WDs with an accuracy >90 per cent, tested in already spectroscopically labelled objects. The excellent performance achieved was extended to practically the whole population of WDs with effective temperatures above 5500 K. Our results show that while the A branch of the Gaia WD Hertzsprung–Russell diagram is practically populated by DA WDs, the B branch is largely formed by non-DAs (65 per cent). The remaining 35 per cent of DAs within the B branch implies a second peak at ∼0.8 M⊙ in the DA mass distribution. Additionally, the Q branch and its extension to lower temperatures can be observed for both DA and non-DA objects due to core crystallization. Finally, we derived a detailed spectral evolution function, which confirms a slow increase of the fraction of non-DAs as the effective temperature decreases down to 10 500 K, where it reaches a maximum of 36 per cent and then decreases for lower temperatures down to ∼31 per cent.
Discovery of the first resolved triple white dwarf Perpinyà-Vallès, M; Rebassa-Mansergas, A; Gänsicke, B T ...
Monthly notices of the Royal Astronomical Society,
02/2019, Letnik:
483, Številka:
1
Journal Article, Publication
Recenzirano
Odprti dostop
We report the discovery of J1953-1019, the first resolved triple white dwarf system.
The triplet consists of an inner white dwarf binary and a wider companion. Using
Gaia DR2 photometry and ...astrometry combined with our follow-up spectroscopy, we
derive effective temperatures, surface gravities, masses and cooling ages of the three
components. All three white dwarfs have pure-hydrogen (DA) atmospheres, masses
of 0.60 - 0.63 M¿ and cooling ages of 40 - 290Myr. We adopt eight initial-to-final
mass relations to estimate the main sequence progenitor masses (which we find to
be similar for the three components, 1.6-2.6M¿) and lifetimes. The differences between the derived cooling times and main sequence lifetimes agree for most of the
adopted initial-to-final mass relations, hence the three white dwarfs in J1953-1019
are consistent with coeval evolution. Furthermore, we calculate the projected orbital
separations of the inner white dwarf binary (303.25±0.01 au) and of the centre of mass
of the inner binary and the outer companion (6 398.97 ± 0.09 au). From these values,
and taking into account a wide range of possible configurations for the triplet to be
currently dynamically stable, we analyse the future evolution of the system. We find
that a collision between the two inner white dwarfs due to Lidov-Kozai oscillations is
unlikely, though if it occurs it could result in a sub-Chandrasekhar Type Ia supernova
explosion.
Peer Reviewed
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