scholarly journals The DECam minute cadence survey – II. 49 variables but no planetary transits of a white dwarf

2019 ◽  
Vol 490 (1) ◽  
pp. 1066-1075 ◽  
Author(s):  
Kyra Dame ◽  
Claudia Belardi ◽  
Mukremin Kilic ◽  
Armin Rest ◽  
A Gianninas ◽  
...  
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Point Sources ◽  
Habitable Zone ◽  
Significant Evidence ◽  
Rr Lyrae ◽  
M Dwarf ◽  
Rule Out ◽  
Planetary Transits

Abstract We present minute cadence photometry of 31 732 point sources observed in one 3 $\rm deg^{2}$ DECam pointing centred at RA = 09:03:02 and Dec. = −04:35:00 over eight consecutive half-nights. We use these data to search for eclipse-like events consistent with a planetary transit of a white dwarf and other sources of stellar variability within the field. We do not find any significant evidence for minute-long transits around our targets, hence we rule out planetary transits around ∼370 white dwarfs that should be present in this field. Additionally, we identify 49 variables, including 40 new systems. These include 23 detached or contact stellar binaries, one eclipsing white dwarf + M dwarf binary, 16 δ Scuti, three RR Lyrae, and two ZZ Ceti pulsators. Results from the remaining two fields in our survey will allow us to place more stringent constraints on the frequency of planets orbiting white dwarfs in the habitable zone.

scholarly journals Polarimetry as a tool to find and characterise habitable planets orbiting white dwarfs

2014 ◽  
Vol 10 (S305) ◽  
pp. 325-332 ◽  
Author(s):  
Luca Fossati ◽  
Stefano Bagnulo ◽  
Carole A. Haswell ◽  
Manish R. Patel ◽  
Richard Busuttil ◽  
...  
Keyword(s):  
Radiation Dose ◽  
Uv Radiation ◽  
Uv Irradiation ◽  
White Dwarf ◽  
White Dwarfs ◽  
Terrestrial Planet ◽  
Habitable Zone ◽  
Habitable Planets ◽  
Earth Like Planets ◽  
M Dwarf

AbstractThere are several ways planets can survive the giant phase of the host star, hence one can consider the case of Earth-like planets orbiting white dwarfs. As a white dwarf cools from 6000 K to 4000 K, a planet orbiting at 0.01 AU from the star would remain in the continuous habitable zone (CHZ) for about 8 Gyr. Polarisation due to a terrestrial planet in the CHZ of a cool white dwarf (CWD) is 102 (104) times larger than it would be in the habitable zone of a typical M-dwarf (Sun-like star). Polarimetry is thus a powerful tool to detect close-in planets around white dwarfs. Multi-band polarimetry would also allow one to reveal the presence of a planet atmosphere, even providing a first characterisation. With current facilities a super-Earth-sized atmosphereless planet is detectable with polarimetry around the brightest known CWD. Planned future facilities render smaller planets detectable, in particular by increasing the instrumental sensitivity in the blue. Preliminary habitability study show also that photosynthetic processes can be sustained on Earth-like planets orbiting CWDs and that the DNA-weighted UV radiation dose for an Earth-like planet in the CHZ is less than the maxima encountered on Earth, hence white dwarfs are compatible with the persistence of complex life from the perspective of UV irradiation.

scholarly journals Interior structures and tidal heating in the TRAPPIST-1 planets

2018 ◽  
Vol 613 ◽  
pp. A37 ◽  
Author(s):  
Amy C. Barr ◽  
Vera Dobos ◽  
László L. Kiss
Keyword(s):  
Heat Fluxes ◽  
Uniform Density ◽  
Generation Model ◽  
Habitable Zone ◽  
Habitable Planet ◽  
Error Bars ◽  
Magma Oceans ◽  
Tidal Heating ◽  
M Dwarf ◽  
Rule Out

Context. With seven planets, the TRAPPIST-1 system has among the largest number of exoplanets discovered in a single system so far. The system is of astrobiological interest, because three of its planets orbit in the habitable zone of the ultracool M dwarf. Aims. We aim to determine interior structures for each planet and estimate the temperatures of their rock mantles due to a balance between tidal heating and convective heat transport to assess their habitability. We also aim to determine the precision in mass and radius necessary to determine the planets’ compositions. Methods. Assuming the planets are composed of uniform-density noncompressible materials (iron, rock, H2O), we determine possible compositional models and interior structures for each planet. We also construct a tidal heat generation model using a single uniform viscosity and rigidity based on each planet’s composition. Results. The compositions for planets b, c, d, and e remain uncertain given the error bars on mass and radius. With the exception of TRAPPIST-1c, all have densities low enough to indicate the presence of significant H2O. Planets b and c experience enough heating from planetary tides to maintain magma oceans in their rock mantles; planet c may have surface eruptions of silicate magma, potentially detectable with next-generation instrumentation. Tidal heat fluxes on planets d, e, and f are twenty times higher than Earth’s mean heat flow. Conclusions. Planets d and e are the most likely to be habitable. Planet d avoids the runaway greenhouse state if its albedo is ≳0.3. Determining the planet’s masses within ~0.1–0.5 Earth masses would confirm or rule out the presence of H2O and/or iron. Understanding the geodynamics of ice-rich planets f, g, and h requires more sophisticated modeling that can self-consistently balance heat production and transport in both rock and ice layers.

scholarly journals A hyper-runaway white dwarf in Gaia DR2 as a Type Iax supernova primary remnant candidate

2019 ◽  
Vol 489 (1) ◽  
pp. 420-426 ◽  
Author(s):  
Nicholas J Ruffini ◽  
Andrew R Casey
Keyword(s):  
White Dwarf ◽  
High Velocity ◽  
White Dwarfs ◽  
Milky Way ◽  
Elemental Abundances ◽  
Type Ia ◽  
Gaia Dr2 ◽  
Rule Out

ABSTRACT Observations of stellar remnants linked to Type Ia and Type Iax supernovae are necessary to fully understand their progenitors. Multiple progenitor scenarios predict a population of kicked donor remnants and partially burnt primary remnants, both moving with relatively high velocity. But only a handful of examples consistent with these two predicted populations have been observed. Here we report the likely first known example of an unbound white dwarf that is consistent with being the fully cooled primary remnant to a Type Iax supernova. The candidate, LP 93-21, is travelling with a galactocentric velocity of $v_{\textrm {gal}} \simeq 605\, {\rm km}\, {\rm s}^{-1}$, and is gravitationally unbound to the Milky Way. We rule out an extragalactic origin. The Type Iax supernova ejection scenario is consistent with its peculiar unbound trajectory, given anomalous elemental abundances are detected in its photosphere via spectroscopic follow-up. This discovery reflects recent models that suggest stellar ejections likely occur often. Unfortunately the intrinsic faintness of white dwarfs, and the uncertainty associated with their direct progenitor systems, makes it difficult to detect and confirm such donors.

scholarly journals A white dwarf bound to the transiting planetary system WASP-98

2020 ◽  
Vol 497 (4) ◽  
pp. 4416-4422
Author(s):  
John Southworth ◽  
Pier-Emmanuel Tremblay ◽  
Boris T Gänsicke ◽  
Daniel Evans ◽  
Teo Močnik
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Planetary System ◽  
Planetary Systems ◽  
Precise Determination ◽  
Spectral Lines ◽  
Low Metallicity ◽  
Gaia Dr2 ◽  
Rule Out

ABSTRACT WASP-98 is a planetary system containing a hot Jupiter transiting a late-G dwarf. A fainter star, 12 arcsec away, has previously been identified as a white dwarf, with a distance and proper motion consistent with a physical association with the planetary system. We present spectroscopy of the white dwarf, with the aim of determining its mass, radius, and temperature and hence the age of the system. However, the spectra show the featureless continuum and lack of spectral lines characteristic of the DC class of white dwarfs. We therefore fitted theoretical white dwarf spectra to the ugriz apparent magnitudes and Gaia DR2 parallax of this object in order to determine its physical properties and the age of the system. We find that the system is old, with a lower limit of 3.6 Gyr, but theoretical uncertainties preclude a precise determination of its age. Its kinematics are consistent with membership of the thick disc, but do not allow us to rule out the thin-disc alternative. The old age and low metallicity of the system suggest that it is subject to an age–metallicity relation, but analysis of the most metal-rich and metal-poor transiting planetary systems yields only insubstantial evidence of this. We conclude that the study of bound white dwarfs can yield independent ages to planetary systems, but such analysis may be better suited to DA and DB rather than DC white dwarfs.

scholarly journals Confirming new white dwarf-ultracool dwarf binary candidates

2020 ◽  
Vol 498 (1) ◽  
pp. 12-24
Author(s):  
M A Hogg ◽  
S L Casewell ◽  
G A Wynn ◽  
E S Longstaff ◽  
I P Braker ◽  
...  
Keyword(s):  
Infrared Spectra ◽  
White Dwarf ◽  
White Dwarfs ◽  
Near Infrared ◽  
Infrared Excess ◽  
Photometric Variability ◽  
Near Infrared Spectra ◽  
Effective Temperatures ◽  
M Dwarf

ABSTRACT We present the results of a study to discover prospective new white dwarf-L dwarf binaries as identified by their near-infrared excesses in the UKIDSS catalogue. We obtained optical spectra to validate the white dwarf nature for 22 of the candidate primary stars, confirming ten as white dwarfs and determining their effective temperatures and gravities. For all 10 white dwarfs, we determined that the near-infrared excess was indeed indicative of a cool companion. Six of these are suggestive of late M dwarf companions, and three are candidate L dwarf companions, with one straddling the M−L boundary. We also present near-infrared spectra of eight additional candidate white dwarf-ultracool dwarf binaries, where the white dwarf primary had been previously confirmed. These spectra indicate one candidate at the M−L boundary, three potential L dwarf companions, and one suspected M dwarf, which showed photometric variability on a ∼6 h period, suggesting the system may be close. Radial velocity follow-up is required to confirm whether these systems are close, or widely separated.

scholarly journals Bayesian constraints on the origin and geology of exo-planetary material using a population of externally polluted white dwarfs

2021 ◽  
Author(s):  
John H D Harrison ◽  
Amy Bonsor ◽  
Mihkel Kama ◽  
Andrew M Buchan ◽  
Simon Blouin ◽  
...  
Keyword(s):  
Solar System ◽  
White Dwarf ◽  
Bayesian Model ◽  
Total Mass ◽  
White Dwarfs ◽  
Bulk Composition ◽  
Planetary Systems ◽  
The Moon ◽  
Planetary Bodies ◽  
Nearby Stars

Abstract White dwarfs that have accreted planetary bodies are a powerful probe of the bulk composition of exoplanetary material. In this paper, we present a Bayesian model to explain the abundances observed in the atmospheres of 202 DZ white dwarfs by considering the heating, geochemical differentiation, and collisional processes experienced by the planetary bodies accreted, as well as gravitational sinking. The majority (>60%) of systems are consistent with the accretion of primitive material. We attribute the small spread in refractory abundances observed to a similar spread in the initial planet-forming material, as seen in the compositions of nearby stars. A range in Na abundances in the pollutant material is attributed to a range in formation temperatures from below 1,000 K to higher than 1,400 K, suggesting that pollutant material arrives in white dwarf atmospheres from a variety of radial locations. We also find that Solar System-like differentiation is common place in exo-planetary systems. Extreme siderophile (Fe, Ni or Cr) abundances in 8 systems require the accretion of a core-rich fragment of a larger differentiated body to at least a 3σ significance, whilst one system shows evidence that it accreted a crust-rich fragment. In systems where the abundances suggest that accretion has finished (13/202), the total mass accreted can be calculated. The 13 systems are estimated to have accreted masses ranging from the mass of the Moon to half that of Vesta. Our analysis suggests that accretion continues for 11Myrs on average.

scholarly journals Direct detection of atomic dark matter in white dwarfs

2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
David Curtin ◽  
Jack Setford
Keyword(s):  
Dark Matter ◽  
Energy Loss ◽  
Cooling Rate ◽  
White Dwarf ◽  
White Dwarfs ◽  
Luminosity Function ◽  
Direct Detection ◽  
Matter Density ◽  
Mixing Parameter ◽  
First Time

Abstract Dark matter could have a dissipative asymmetric subcomponent in the form of atomic dark matter (aDM). This arises in many scenarios of dark complexity, and is a prediction of neutral naturalness, such as the Mirror Twin Higgs model. We show for the first time how White Dwarf cooling provides strong bounds on aDM. In the presence of a small kinetic mixing between the dark and SM photon, stars are expected to accumulate atomic dark matter in their cores, which then radiates away energy in the form of dark photons. In the case of white dwarfs, this energy loss can have a detectable impact on their cooling rate. We use measurements of the white dwarf luminosity function to tightly constrain the kinetic mixing parameter between the dark and visible photons, for DM masses in the range 10−5–105 GeV, down to values of ϵ ∼ 10−12. Using this method we can constrain scenarios in which aDM constitutes fractions as small as 10−3 of the total dark matter density. Our methods are highly complementary to other methods of probing aDM, especially in scenarios where the aDM is arranged in a dark disk, which can make direct detection extremely difficult but actually slightly enhances our cooling constraints.

scholarly journals The most massive white dwarfs in the solar neighbourhood

2021 ◽  
Vol 503 (4) ◽  
pp. 5397-5408
Author(s):  
Mukremin Kilic ◽  
P Bergeron ◽  
Simon Blouin ◽  
A Bédard
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Transverse Velocity ◽  
Maximum Mass ◽  
Model Calculations ◽  
Rapid Rotation ◽  
Rotation Rates ◽  
Binary Mergers ◽  
Chandrasekhar Limit

ABSTRACT We present an analysis of the most massive white dwarf candidates in the Montreal White Dwarf Database 100 pc sample. We identify 25 objects that would be more massive than $1.3\, {\rm M}_{\odot }$ if they had pure H atmospheres and CO cores, including two outliers with unusually high photometric mass estimates near the Chandrasekhar limit. We provide follow-up spectroscopy of these two white dwarfs and show that they are indeed significantly below this limit. We expand our model calculations for CO core white dwarfs up to M = 1.334 M⊙, which corresponds to the high-density limit of our equation-of-state tables, ρ = 109 g cm−3. We find many objects close to this maximum mass of our CO core models. A significant fraction of ultramassive white dwarfs are predicted to form through binary mergers. Merger populations can reveal themselves through their kinematics, magnetism, or rapid rotation rates. We identify four outliers in transverse velocity, four likely magnetic white dwarfs (one of which is also an outlier in transverse velocity), and one with rapid rotation, indicating that at least 8 of the 25 ultramassive white dwarfs in our sample are likely merger products.

scholarly journals The McDonald Observatory search for pulsating sdA stars

2018 ◽  
Vol 617 ◽  
pp. A6 ◽  
Author(s):  
K. J. Bell ◽  
I. Pelisoli ◽  
S. O. Kepler ◽  
W. R. Brown ◽  
D. E. Winget ◽  
...  
Keyword(s):  
Time Series ◽  
White Dwarfs ◽  
Main Sequence ◽  
Pulsating Stars ◽  
Blue Stragglers ◽  
Rr Lyrae ◽  
Stellar Pulsations ◽  
Low Mass ◽  
New Variables

Context. The nature of the recently identified “sdA” spectroscopic class of stars is not well understood. The thousands of known sdAs have H-dominated spectra, spectroscopic surface gravity values between main sequence stars and isolated white dwarfs, and effective temperatures below the lower limit for He-burning subdwarfs. Most are likely products of binary stellar evolution, whether extremely low-mass white dwarfs and their precursors or blue stragglers in the halo. Aims. Stellar eigenfrequencies revealed through time series photometry of pulsating stars sensitively probe stellar structural properties. The properties of pulsations exhibited by sdA stars would contribute substantially to our developing understanding of this class. Methods. We extend our photometric campaign to discover pulsating extremely low-mass white dwarfs from the McDonald Observatory to target sdA stars classified from SDSS spectra. We also obtain follow-up time series spectroscopy to search for binary signatures from four new pulsators. Results. Out of 23 sdA stars observed, we clearly detect stellar pulsations in 7. Dominant pulsation periods range from 4.6 min to 12.3 h, with most on timescales of approximately one hour. We argue specific classifications for some of the new variables, identifying both compact and likely main sequence dwarf pulsators, along with a candidate low-mass RR Lyrae star. Conclusions. With dominant pulsation periods spanning orders of magnitude, the pulsational evidence supports the emerging narrative that the sdA class consists of multiple stellar populations. Since multiple types of sdA exhibit stellar pulsations, follow-up asteroseismic analysis can be used to probe the precise evolutionary natures and stellar structures of these individual subpopulations.

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