Diamonds in the Sky!

2019 ◽  
pp. 101-109
Author(s):  
Nicholas Mee
Keyword(s):  
Nuclear Fuel ◽  
White Dwarf ◽  
White Dwarfs ◽  
Star Trek ◽  
The Sun ◽  
New Class ◽  
The Earth ◽  
Night Sky

After consuming their nuclear fuel, most stars lose their outer envelopes and all that remains is the collapsed core of the star, an object known as a white dwarf. Ever since Galileo pointed a telescope at the night sky, each advance in telescope making has resulted in sensational discoveries. Alvan Clark & Sons ground some of the biggest telescope lenses ever made. Alvan Graham Clark discovered Sirius B while testing one of these lenses. Eddington deduced that Sirius B has a size similar to that of the Earth, but with the mass of the Sun, and was an example of a new class of stars—white dwarfs. The easiest white dwarf to see with a telescope orbits the star Keid. In Star Trek, the planet Vulcan orbits the star Keid A.

scholarly journals Hot DQ white dwarfs: a pulsational test of the mixing scenario for their formation

2009 ◽  
Vol 5 (H15) ◽  
pp. 370-370
Author(s):  
A. Romero ◽  
A. H. Córsico ◽  
L. G. Althaus ◽  
E. García-Berro
Keyword(s):  
Stability Analysis ◽  
White Dwarf ◽  
White Dwarfs ◽  
Evolutionary Models ◽  
Instability Strip ◽  
Dwarf Stars ◽  
Photometric Variability ◽  
New Class ◽  
White Dwarf Stars ◽  
Born Again

Hot DQ white dwarfs constitute a new class of white dwarf stars, uncovered recently within the framework of SDSS project. There exist nine of them, out of a total of several thousands white dwarfs spectroscopically identified. Recently, three hot DQ white dwarfs have been reported to exhibit photometric variability with periods compatible with pulsation g-modes. In this contribution, we presented the results of a non-adiabatic pulsation analysis of the recently discovered carbon-rich hot DQ white dwarf stars. Our study relies on the full evolutionary models of hot DQ white dwarfs recently developed by Althaus et al. (2009), that consistently cover the whole evolution from the born-again stage to the white dwarf cooling track. Specifically, we performed a stability analysis on white dwarf models from stages before the blue edge of the DBV instability strip (Teff ≈ 30000 K) until the domain of the hot DQ white dwarfs (18000-24000 K), including the transition DB→hot DQ white dwarf. We explore evolutionary models with M*= 0.585M⊙ and M* = 0.87M⊙, and two values of thickness of the He-rich envelope (MHe = 2 × 10−7M* and MHe = 10−8M*).

scholarly journals The High Resolution Spectrum of the Pulsating, Pre-White Dwarf Star PG 1159-035 (GW VIR)

1989 ◽  
Vol 114 ◽  
pp. 384-387
Author(s):  
James Liebert ◽  
F. Wesemael ◽  
D. Husfeld ◽  
R. Wehrse ◽  
S. G. Starrfield ◽  
...  
Keyword(s):  
High Resolution ◽  
Effective Temperature ◽  
White Dwarf ◽  
White Dwarfs ◽  
High Resolution Spectrum ◽  
Dwarf Star ◽  
Dwarf Stars ◽  
New Class ◽  
White Dwarf Stars ◽  
Nonradial Pulsation

First reported at the IAU Colloquium No. 53 on White Dwarfs (McGraw et al. 1979), PG 1159-035 (GW Vir) is the prototype of a new class of very hot, pulsating, pre-white dwarf stars. It shows complicated, nonradial pulsation modes which have been studied exhaustively, both observationally and theoretically. The effective temperature has been crudely estimated as 100,000 K with log g ~ 7 (Wesemael, Green and Liebert 1985, hereafter WGL).

scholarly journals White Dwarf Seismology: Inverse Problem of g-Mode Oscillations

1988 ◽  
Vol 108 ◽  
pp. 86-87
Author(s):  
Hiromoto Shibahashi ◽  
Takashi Sekii ◽  
Steven Kawaler
Keyword(s):  
Inverse Problem ◽  
Internal Structure ◽  
White Dwarf ◽  
White Dwarfs ◽  
Research Field ◽  
The Sun ◽  
Pulsating Stars ◽  
Low Degree ◽  
Physical Quantities ◽  
Light Variability

Since light variability in white dwarfs was first discovered twenty years ago, eighteen DA white dwarfs, several pulsating DB white dwarfs, and hotter pre-white dwarfs have so far been found to be pulsating variables. The most conspicuous characteristics of pulsations in these stars are that they seem to consist of multiple g-modes of nonradial oscillations. Attention should be paid to multiplicity of modes. Stimulated by the success of helioseimology, a research field called ‘asteroseismology’, in which we may probe the internal structure of stars by means of observations of their oscillations, is going to develop. How well such a seismological approach succeeds is dependent on how many modes are observed in each of stars. Since the number of modes of an individual pulsating white dwarf is larger than those of other types of pulsating stars but for the Sun, the seismological study may be the most promising as to the white dwarfs. In fact, by applying the asymptotic relations among eigenfrequencies of high order g-modes with low degree, the degreel, and the radial ordern, Kawaler(1987a,b,c) succeeded to get some constraints on the physical quantities of some of pulsating white dwarfs.

Seismic Inversions for White Dwarf Stars

2002 ◽  
Vol 185 ◽  
pp. 606-607
Author(s):  
M. Takata ◽  
M.H. Montgomery
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
The Sun ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Inversion Methods ◽  
Space Observations

AbstractInversion methods have been used successfully for the Sun. The stars with the next richest set of observed frequencies are the white dwarfs. We consider here the viability of numerical inversions for these stars. We find that, while the number of presently observed modes in the white dwarf GD 358 is too small for structural inversions, such inversions would be possible if the frequencies of all modes with 1 ≤ l ≤ 3 were observed. This is possible for space observations by e.g. Eddington.

Heavenly Bodies

2019 ◽  
Author(s):  
Peter Wothers
Keyword(s):  
Seventeenth Century ◽  
Sixteenth Century ◽  
The Sun ◽  
The Moon ◽  
The Earth ◽  
Night Sky ◽  
The Universe ◽  
Over Time

We don’t know for sure where the names of the longest-known elements come from, but a connection was made early on between the most ancient metals and bodies visible in the heavens. Figure 1 shows an engraving from a seventeenth-century text with the title ‘The Seven Metals’ (translated from the Latin). It isn’t immediately obvious how the image is meant to depict seven metals until we explore the connections between alchemy and astronomy. However strange such associations seem to us now, we shall see that new elements named in the eighteenth, nineteenth, twentieth, and twenty-first centuries have had astronomical origins. We can’t properly understand why some of the more recent elements were named as they were without first understanding these earlier historical connections. As we look into the night sky, the distant stars remain in their same relative positions and seem to move gracefully together through the heavens. Of course, we now know that it is the spinning Earth that gives this illusion of movement. The imaginations of our ancestors joined the bright dots to pick out fanciful patterns such as the Dragon, the Dolphin, or the Great Bear—the latter being more often known today (with rather less imagination) as the Big Dipper, the Plough, or even the Big Saucepan. But, while these patterns, the constellations, remained unchanging over time, there were seven objects, or ‘heavenly bodies’, that seemed to move across the skies with a life of their own. They were given the name ‘planet’, which derives from the Greek word for ‘wanderer’ (‘planetes asteres’, ‘πλάνητες ἀστέρες’, meaning ‘wandering stars’). These seven bodies were the Sun, the Moon, Mercury, Venus, Mars, Jupiter, and Saturn, all of which were documented by the Babylonians over three thousand years ago. Until the sixteenth century, the most commonly held view was that the Earth was at the centre of the Universe and that the seven bodies revolved around the Earth, with the relative orbits shown schematically in Figure 2.

scholarly journals Structure and Composition of White Dwarf Atmospheres and Convection Zones

1979 ◽  
Vol 53 ◽  
pp. 223-244
Author(s):  
K.H. Böhm
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Energy Transport ◽  
Practical Interest ◽  
Surface Flux ◽  
Surface Fluxes ◽  
The Sun ◽  
Surface Cooling ◽  
Additional Energy ◽  
Basic Properties

SummaryWe present a brief review of the basic properties of white dwarf atmospheres) convection zones and corona models emphasizing qualitative and intuitive aspects.1. Atmospheres: We restrict our discussion essentially to very hot and very cool atmospheres since these are especially interesting. With regard to the first type of objects we study the fundamental differences between DA and non-DA models and between their surface fluxes. We discuss the important role of electron scattering in determining the EUV spectra of these objects. The differences between DAs and non-DAs with regard to backwarming effect and surface cooling are summarized.In our discussion of very cool non-DA atmospheres we emphasize the importance of the additional energy transport mechanisms convection and conduction which should both be very effective for Teff < 4000K and which lead to a very flat temperature gradient. This small gradient must lead to a rather featureless surface flux.2. Convection Zones. After a survey of the basic numerical results in this field we investigate the question whether convection in white dwarfs has the same basic properties as convection in other stars. We find that contrary to intuitive expectations the Rayleigh number in very cool non-DAs is higher than in the sun (indicating very turbulent convection). The Prandtl number in these objects is 6 to 7 orders of magnitude higher than in the sun.3. Coronae. The basic methods of the calculation of coronae for white dwarfs are very briefly discussed. We present some results for DA and non-DA stars from unpublished work by D.O. Muchmore and the author. It uses revised values for the emissivities. Only non-DA coronae are of practical interest. DA coronae have much lower densities and temperatures. White dwarf coronae do not generate a stellar wind.

Propellers — A New Class of Interacting Binaries

1996 ◽  
Vol 165 ◽  
pp. 451-456 ◽  
Author(s):  
M. Mikołajewski ◽  
J. Mikołajewska ◽  
T. Tomov
Keyword(s):  
White Dwarf ◽  
High Velocity ◽  
White Dwarfs ◽  
New Class ◽  
Symbiotic Binaries

CH Cyg and MWC 560 are very peculiar symbiotic binaries consisting of an M giant and a white-dwarf companion. The systems have many features in common. In particular, both show occasional eruptions with sub-Eddington luminosity accompanied by flickering activity, and appearance of high-velocity jets. We present arguments that objects like CH Cyg and MWC 560 form a new subclass of interacting binaries distinguished by the presence of wind accreting magnetic white dwarfs.

scholarly journals 17. On the Origin of White Dwarfs

1971 ◽  
Vol 42 ◽  
pp. 124-124
Author(s):  
B. Paczyński
Keyword(s):  
Nuclear Fuel ◽  
White Dwarf ◽  
White Dwarfs ◽  
Planetary Nebulae ◽  
Small Mass ◽  
Dynamical Instability ◽  
Helium Burning ◽  
Large Depth ◽  
Almost All

Model evolutionary calculations have been made for population I stars (X = 0.7, Z = 0.03) with masses of 0.8, 1.5, 3, 5, 7, 10, and 15 M⊙ (Paczyński, 1970). Neutrino losses were taken into account. All the models were evolved up to the red supergiant phase with the hydrogen and helium burning shell sources. In this phase of evolution the hydrogen rich envelopes of 0.8, 1.5, and 3 M⊙ stars became dynamically unstable due to the large depth of the hydrogen and helium ionization zones. It was assumed that almost entire envelopes were lost as a result of that instability. The degenerate carbon-oxygen cores of 0.6, 0.8, and 1.2 M⊙ were left with the hydrogen rich envelopes of a small mass. Almost all the hydrogen that was left was subsequently burnt in the shell source. Finally, the hydrogen and helium burning shell sources disappeared as the nuclear fuel was exhausted. The models were cooling down to the white dwarf phase and they had a small amount of hydrogen left close to their surfaces. It is estimated that population I stars with masses up to 3.5 M⊙ may produce white dwarfs with masses up to 1.37 M⊙. The hydrogen rich envelopes that were lost as a result of dynamical instability could form planetary nebulae with masses up to 2 M⊙. Further details are published in the paper referred to above.

scholarly journals White Dwarf Probes of Interstellar Deuterium

2000 ◽  
Vol 198 ◽  
pp. 485-486
Author(s):  
Wayne Landsman
Keyword(s):  
High Resolution ◽  
Interstellar Medium ◽  
White Dwarf ◽  
White Dwarfs ◽  
Accurate Determination ◽  
The Sun ◽  
Local Interstellar Medium ◽  
Space Telescope ◽  
Imaging Spectrograph

We review the advantages of using hot white dwarfs (WDs) as probes of the deuterium abundance in the local interstellar medium. We then discuss advantages of the Space Telescope Imaging Spectrograph (STIS) for such observations, as compared with earlier observations with the Goddard High Resolution Spectrograph (GHRS). The GHRS Ly α profile of the white dwarf HZ 43 is probably modified by the hot ‘hydrogen wall’ surrounding the Sun; but despite this complication, the sightline remains a promising one for an accurate determination of the deuterium abundance in the local interstellar medium.

Seti Space Missions

1997 ◽  
Vol 161 ◽  
pp. 761-776 ◽  
Author(s):  
Claudio Maccone
Keyword(s):  
Electromagnetic Waves ◽  
Space Missions ◽  
Gravitational Lens ◽  
The Sun ◽  
Space Antenna ◽  
Focal Distance ◽  
Large Space ◽  
The Earth ◽  
Space Antennas ◽  
New Space

AbstractSETI from space is currently envisaged in three ways: i) by large space antennas orbiting the Earth that could be used for both VLBI and SETI (VSOP and RadioAstron missions), ii) by a radiotelescope inside the Saha far side Moon crater and an Earth-link antenna on the Mare Smythii near side plain. Such SETIMOON mission would require no astronaut work since a Tether, deployed in Moon orbit until the two antennas landed softly, would also be the cable connecting them. Alternatively, a data relay satellite orbiting the Earth-Moon Lagrangian pointL2would avoid the Earthlink antenna, iii) by a large space antenna put at the foci of the Sun gravitational lens: 1) for electromagnetic waves, the minimal focal distance is 550 Astronomical Units (AU) or 14 times beyond Pluto. One could use the huge radio magnifications of sources aligned to the Sun and spacecraft; 2) for gravitational waves and neutrinos, the focus lies between 22.45 and 29.59 AU (Uranus and Neptune orbits), with a flight time of less than 30 years. Two new space missions, of SETI interest if ET’s use neutrinos for communications, are proposed.

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