Observation data Epoch J2000.0 Equinox J2000.0 | |
---|---|
Constellation | Pisces |
Right ascension | 23h 28m 47.6365s [1] |
Declination | +05° 14′ 54.235″ [1] |
Apparent magnitude (V) | 13.03 [2] |
Characteristics | |
Spectral type | DAV4.4 [2] |
U−B color index | −0.63 [2] |
B−V color index | 0.14 [2] |
V−R color index | 0.0 [3] |
R−I color index | 0.2 [3] |
Variable type | DAV (ZZ Ceti) [2] |
Astrometry | |
Radial velocity (Rv) | 15.3 ± 3.0 [3] km/s |
Proper motion (μ) | RA: −398.246(32) mas/yr [1] Dec.: −266.744(20) mas/yr [1] |
Parallax (π) | 57.0620 ± 0.0251 mas [1] |
Distance | 57.16 ± 0.03 ly (17.525 ± 0.008 pc) |
Details | |
Mass | 0.70 ± 0.03 [4] M☉ |
Radius | 0.01 [5] R☉ |
Luminosity (bolometric) | 0.002 [4] L☉ |
Surface gravity (log g) | 8.15 ± 0.05 [4] cgs |
Temperature | 11,820 ± 175 [4] K |
Other designations | |
Database references | |
SIMBAD | data |
Giclas 29-38, also known as ZZ Piscium, is a variable white dwarf star of the DAV (or ZZ Ceti) type, whose variability is due to large-amplitude, non-radial pulsations known as gravity waves. It was first reported to be variable by Shulov and Kopatskaya in 1974. [6] [7] DAV stars are like normal white dwarfs but have luminosity variations with amplitudes as high as 30%, arising from a superposition of vibrational modes with periods from 100 to 1,000 seconds. Large-amplitude DAVs generally differ from lower-amplitude DAVs by having lower temperatures, longer primary periodicities, and many peaks in their vibrational spectra with frequencies which are sums of other vibrational modes. [8]
G29-38, like other complex, large-amplitude DAV variables, has proven difficult to understand. The power spectrum or periodogram of the light curve varies over times which range from weeks to years. Usually, one strong mode dominates, although many smaller-amplitude modes are often observed. The larger-amplitude modes, however, fluctuate in and out of observability; some low-power areas show more stability. Asteroseismology uses the observed spectrum of pulsations from stars like G29-38 to infer the structure of their interiors. [8]
The circumstellar environment of G29-38 first attracted attention in the late 1980s during a near-infrared survey of 200 white dwarfs conducted by Ben Zuckerman and Eric Becklin to search for low mass companion stars and brown dwarfs. [10] G29-38 was shown to radiate substantial emission between 2 and 5 micrometres, far in excess of that expected from extrapolation of the visual and near infrared spectrum of the star. [11] Like other young, hot white dwarfs, G29-38 is thought to have formed relatively recently (600 million years ago) from its AGB progenitor, and therefore the excess was naturally explained by emission from a Jupiter-like brown dwarf with a temperature of 1200 K and a radius of 0.15 solar radius. [10] [11] However, later observations, including speckle interferometry, failed to detect a brown dwarf. [12]
Infrared observations made in 2004 by NASA's Spitzer Space Telescope indicated the presence of a dust cloud around G29-38, which may have been created by tidal disruption of an exocomet or exoasteroid passing close to the white dwarf. [13] This may mean that G29-38 is still orbited by a ring of surviving comets and, possibly, outer planets. This is the first observation supporting the idea that comets persist to the white dwarf stage of stellar evolution. [14]
Infrared emission at 9-11 Mircons from Spitzer spectroscopy were interpreted as a mixture of amorphous olivine and a small amount of fosterite in the disk. [13] Modelling of the disk have shown that the inner edge of the disk lies at around 96±4 white dwarf radii and that the disk has a width of about 1-10 white dwarf radii. The dust mass of the disk is about 4-5 x 1018 g (about half the mass of a massive asteroid) and the disk has a temperature less than 1000 K. [15]
A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to Earth's. A white dwarf's low luminosity comes from the emission of residual thermal energy; no fusion takes place in a white dwarf. The nearest known white dwarf is Sirius B, at 8.6 light years, the smaller component of the Sirius binary star. There are currently thought to be eight white dwarfs among the hundred star systems nearest the Sun. The unusual faintness of white dwarfs was first recognized in 1910. The name white dwarf was coined by Willem Luyten in 1922.
Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main-sequence stars. Their mass is approximately 13 to 80 times that of Jupiter (MJ)—not big enough to sustain nuclear fusion of ordinary hydrogen (1H) into helium in their cores, but massive enough to emit some light and heat from the fusion of deuterium (2H). The most massive ones can fuse lithium (7Li).
A variable star is a star whose brightness as seen from Earth changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as either:
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HD 210277 is a single star in the equatorial constellation of Aquarius. It has an apparent visual magnitude of 6.54, which makes it a challenge to view with the naked eye, but it is easily visible in binoculars. The star is located at a distance of 69.6 light years from the Sun based on parallax, but is drifting closer with a radial velocity of −20.9 km/s.
Eta Telescopii is a white-hued star in the southern constellation of Telescopium. This is an A-type main sequence star with an apparent visual magnitude of +5.03. It is approximately 158 light years from Earth and is a member of the Beta Pictoris Moving Group of stars that share a common motion through space. It is moving through the Galaxy at a speed of 23.7 km/s relative to the Sun.
HL Tau 76 is a variable white dwarf star of the DAV type. It was observed by G. Haro and W. J. Luyten in 1961, and was the first variable white dwarf discovered when, in 1968, Arlo U. Landolt found that it varied in brightness with a period of approximately 749.5 seconds, or 12.5 minutes. Like other DAV white dwarfs, its variability arises from non-radial gravity wave pulsations within itself., § 7. Later observation and analysis has found HL Tau 76 to pulsate in over 40 independent vibrational modes, with periods between 380 seconds and 1390 seconds.
A pulsating white dwarf is a white dwarf star whose luminosity varies due to non-radial gravity wave pulsations within itself. Known types of pulsating white dwarfs include DAV, or ZZ Ceti, stars, with hydrogen-dominated atmospheres and the spectral type DA; DBV, or V777 Her, stars, with helium-dominated atmospheres and the spectral type DB; and GW Vir stars, with atmospheres dominated by helium, carbon, and oxygen, and the spectral type PG 1159. GW Vir stars may be subdivided into DOV and PNNV stars; they are not, strictly speaking, white dwarfs but pre-white dwarfs which have not yet reached the white dwarf region on the Hertzsprung-Russell diagram. A subtype of DQV stars, with carbon-dominated atmospheres, has also been proposed, and in May 2012, the first extremely low mass variable (ELMV) white dwarf was reported.
G117-B15A is a small, well-observed variable white dwarf star of the DAV, or ZZ Ceti, type in the constellation of Leo Minor.
Ross 548 is a white dwarf in the equatorial constellation of Cetus. With a mean apparent visual magnitude of 14.2 it is much too faint to be visible to the naked eye. Based on parallax measurements, it is located at a distance of 107 light years from the Sun. It was found to be variable in 1970 and in 1972 it was given the variable star designation ZZ Ceti. This is a pulsating white dwarf of the DAV type that is the prototype of the ZZ Ceti variable class., pp. 891, 895.
GD 362 is a white dwarf approximately 150 light years from Earth. In 2004, spectroscopic observations showed that it had a relatively high concentration of metals in its atmosphere. Since the high gravitational field of white dwarfs quickly forces heavy elements to settle towards the bottom of the atmosphere, this meant that the atmosphere was being polluted by an external source. In 2005, infrared photometric observations suggested that it was surrounded by a ring of dust with size comparable to the rings of Saturn, providing an explanation for this pollution.
HR 4796 is a binary star system in the southern constellation of Centaurus. Parallax measurements put it at a distance of 235 light-years from the Earth. The two components of this system have an angular separation of 7.7 arcseconds, which, at their estimated distance, is equivalent to a projected separation of about 560 Astronomical Units (AU), or 560 times the separation of the Earth from the Sun. The star and its ring resemble an eye, and it is sometimes known by the nickname "Sauron's Eye".
HR 8799 is a roughly 30 million-year-old main-sequence star located 133.3 light-years away from Earth in the constellation of Pegasus. It has roughly 1.5 times the Sun's mass and 4.9 times its luminosity. It is part of a system that also contains a debris disk and at least four massive planets. Those planets, along with Fomalhaut b, were the first exoplanets whose orbital motion was confirmed by direct imaging. The star is a Gamma Doradus variable: its luminosity changes because of non-radial pulsations of its surface. The star is also classified as a Lambda Boötis star, which means its surface layers are depleted in iron peak elements. It is the only known star which is simultaneously a Gamma Doradus variable, a Lambda Boötis type, and a Vega-like star.
WISEPC J140518.40+553421.4 is a brown dwarf of spectral class Y0 (pec?), located in constellation Ursa Major at approximately 25.3 light-years from Earth. It is one of the Sun's nearest neighbors.
GD 165 is a system of a white dwarf and a brown dwarf of spectral types DA4 + L4, located in constellation Boötes at approximately 103 light-years from Earth. GD 165 B remained the only brown dwarf companion of a white dwarf until the discovery of GD 1400 B, which was discovered 17 years later.
HN Pegasi is the variable star designation for a young, Sun-like star in the northern constellation of Pegasus. It has an apparent visual magnitude of 5.9, which, according to the Bortle scale, indicates that it is visible to the naked eye from suburban skies. Parallax measurements put the star at a distance of around 59 light years from the Sun, but it is drifting closer with a radial velocity of −16.7 km/s.
IK Tauri or NML Tauri is a Mira variable star located about 280 parsecs (910 ly) from the Sun in the zodiac constellation of Taurus.
Backyard Worlds: Planet 9 is a NASA-funded citizen science project which is part of the Zooniverse web portal. It aims to discover new brown dwarfs, faint objects that are less massive than stars, some of which might be among the nearest neighbors of the Solar System, and might conceivably detect the hypothesized Planet Nine. The project's principal investigator is Marc Kuchner, an astrophysicist at NASA's Goddard Space Flight Center.
WD 0145+234 is a white dwarf star approximately 95 ly (29 pc) from Earth in the constellation of Aries that has been associated with studies suggesting that a very large exoasteroid near the star was substantially disrupted, resulting in a considerable amount of dust and debris around the star. Alternatively, the outburst around WD 0145+234 is explained with ongoing collisions between planetesimals inside the dusty debris disk around the white dwarf.
An exoasteroid, exo-asteroid or extrasolar asteroid, is an asteroid outside the Solar System. Exoasteroids were considered to be hypothetical, but scientific study and thorough analysis has provided evidence for their existence.