GD 358 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 DBV type. Like other

pulsating white dwarf 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 s ...

s, its variability arises from non-radial

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 ...

pulsations within the star itself. GD 358 was discovered during the 1958–1970

Lowell Observatory Lowell Observatory is an astronomical observatory in Flagstaff, Arizona, United States. Lowell Observatory was established in 1894, placing it among the oldest observatories in the United States, and was designated a National Historic Landmark ...

survey for high

proper motion Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...

stars in the

Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...

. Although it did not have high proper motion, it was noticed that it was a very blue star, and hence might be a

. Greenstein confirmed this in 1969. In 1968,

Arlo U. Landolt Arlo Udell Landolt (September 29, 1935 – January 21, 2022) was an American astronomer known for his widely used photometric standards. Life and career Early life Landolt was born in Highland, Illinois to farmers Arlo M. Landolt and Vesta K ...

discovered the first intrinsically

when he found that

HL Tau 76 HL Tau 76 is a variable white dwarf star of the DAV (or ZZ Ceti) 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 br ...

varied in brightness with a period of approximately 749.5 seconds, or 12.5 minutes.A New Short-Period Blue Variable
Arlo U. Landolt, ''Astrophysical Journal'' 153, #1 (July 1968), pp. 151–164. By the middle of the 1970s, a number of additional variable white dwarfs had been found, but, like HL Tau 76, they were all white dwarfs of spectral type DA, with

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

-dominated atmospheres. In 1982, calculations by

Don Winget Don E. Winget is an American astronomer and astrophysicist who studies white dwarf stars. He is the Harlan J. Smith Centennial Professor in Astronomy and a university distinguished teaching professor at the University of Texas at Austin. Resear ...

and his coworkers suggested that helium-atmosphere DB white dwarfs with surface temperatures around 19,000 K should also pulsate.Hydrogen-driving and the blue edge of compositionally stratified ZZ Ceti star models
D. E. Winget, H. M. van Horn, M. Tassoul, G. Fontaine, C. J. Hansen, and B. W. Carroll, ''Astrophysical Journal'' 252 (January 15, 1982), pp. L65–L68.^{, p. L67.} Winget then searched for such stars and found that GD 358 was a variable DB, or '' DBV'', white dwarf.Photometric observations of GD 358: DB white dwarfs do pulsate
D. E. Winget, E. L. Robinson, R. D. Nather, and G. Fontaine, ''Astrophysical Journal'' 262 (November 1, 1982), pp. L11–L15. This was the first prediction of a class of variable stars before their observation.White Dwarf Stars, Steven D. Kawaler, in ''Stellar remnants'', S. D. Kawaler, I. Novikov, and G. Srinivasan, edited by Georges Meynet and Daniel Schaerer, Berlin: Springer, 1997. Lecture notes for Saas-Fee advanced course number 25. .^{, p. 89.} In 1985, this star was given the variable-star designation ''V777 Herculis'', which is also another name for this class of variable stars.The 67th Name-List of Variable Stars
P. N. Kholopov, N. N. Samus, E. V. Kazarovets, and N. B. Perova, ''Information Bulletin on Variable Stars'', #2681, March 8, 1985.^;White dwarfs, Gilles Fontaine and François Wesemael, in ''Encyclopedia of Astronomy and Astrophysics'', ed. Paul Murdin, Bristol and Philadelphia: Institute of Physics Publishing and London, New York and Tokyo: Nature Publishing Group, 2001. .^{, p. 3525}

Notes and references

{{DEFAULTSORT:GD 358 Hercules (constellation) Pulsating white dwarfs Herculis, V777