Giclas 29-38, also known as ZZ Piscium, is a

variable Variable may refer to: * Variable (computer science), a symbolic name associated with a value and whose associated value may be changed * Variable (mathematics), a symbol that represents a quantity in a mathematical expression, as used in many ...

white dwarf 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 the Earth's. A white dwarf's faint luminosity comes fro ...

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

of the DAV (or ZZ Ceti) type, whose variability is due to large-amplitude, non-radial pulsations known as

gravity wave In fluid dynamics, gravity waves are waves generated in a fluid medium or at the interface between two media when the force of gravity or buoyancy tries to restore equilibrium. An example of such an interface is that between the atmosphere ...

s. It was first reported to be variable by Shulov and Kopatskaya in 1974. DAV stars are like normal white dwarfs but have

luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...

variations with amplitudes as high as 30%, arising from a superposition of

vibrational modes A normal mode of a dynamical system is a pattern of motion in which all parts of the system move sinusoidally with the same frequency and with a fixed phase relation. The free motion described by the normal modes takes place at fixed frequencies. ...

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 mode A normal mode of a dynamical system is a pattern of motion in which all parts of the system move sinusoidally with the same frequency and with a fixed phase relation. The free motion described by the normal modes takes place at fixed frequencies. ...

s.Observational limits on companions to G29-38
S. J. Kleinman, R. E. Nather, D. E. Winget, J. C. Clemens, P. A. Bradley, A. Kanaan, J. L. Provencal, C. F. Claver, T. K. Watson, K. Yanagida, J. S. Dixson, M. A. Wood, D. J. Sullivan, E. Meistas, E. M. Leibowitz, P. Moskalik, S. Zola, G. Pajdosz, J. Krzesinski, J.-E. Solheim, A. Bruvold, D. O'Donoghue, M. Katz, G. Vauclair, N. Dolez, M. Chevreton, M. A. Barstow, S. O. Kepler, O. Giovannini, C. J. Hansen, and S. D. Kawaler, ''Astrophysical Journal'' 436, #2 (December 1994), pp. 875–884. ZZPscLightCurve

G29-38, like other complex, large-amplitude DAV variables, has proven difficult to understand. The power

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...

periodogram In signal processing, a periodogram is an estimate of the spectral density of a signal. The term was coined by Arthur Schuster in 1898. Today, the periodogram is a component of more sophisticated methods (see spectral estimation). It is the most co ...

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 Asteroseismology or astroseismology is the study of oscillations in stars. Stars have many resonant modes and frequencies, and the path of sound waves passing through a star depends on the speed of sound, which in turn depends on local temperature ...

uses the observed spectrum of pulsations from stars like G29-38 to infer the structure of their interiors.

Debris disk

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 Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most m ...

.A low-temperature companion to a white dwarf star
E. E. Becklin & B. Zuckerman, ''Nature'' 336 (Dec. 15, 1988), pp. 656-658 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.Excess infrared radiation from a white dwarf - an orbiting brown dwarf?
B. Zuckerman & E. E. Becklin, ''Nature'' 330, (Nov. 12, 1987), pp. 138-140 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 Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...

-like brown dwarf with a temperature of 1200 K and a radius of 0.15

solar radius Solar radius is a unit of distance used to express the size of stars in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: :1\,R_ = 6.957\tim ...

. However, later observations, including

speckle interferometry Speckle imaging describes a range of high-resolution astronomical imaging techniques based on the analysis of large numbers of short exposures that freeze the variation of atmospheric turbulence. They can be divided into the shift-and-add ("''i ...

, failed to detect a brown dwarf. Infrared observations made in 2004 by

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

Spitzer Space Telescope The Spitzer Space Telescope, formerly the Space Infrared Telescope Facility (SIRTF), was an infrared space telescope launched in 2003. Operations ended on 30 January 2020. Spitzer was the third space telescope dedicated to infrared astronomy, f ...

indicated the presence of a dust cloud around G29-38, which may have been created by tidal disruption of an

exocomet An exocomet, or extrasolar comet, is a comet outside the Solar System, which includes rogue comets and comets that orbit stars other than the Sun. The first exocomets were detected in 1987 around Beta Pictoris, a very young A-type main-sequence ...

passing close to the white dwarf. This may mean that G29-38 is still

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

ed by a ring of surviving comets and, possibly,

outer planet The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...

s. This is the first observation supporting the idea that

comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ar ...

s persist to the white dwarf stage of

stellar evolution Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is cons ...

.NASA's Spitzer Finds Possible Comet Dust Around Dead Star
NASA press release, January 11, 2006.

References

External links

* {{DEFAULTSORT:G 29-38 Pulsating white dwarfs Pisces (constellation) Piscium, ZZ