GD 358
Encyclopedia
GD 358 is a variable
white dwarf
star
of the DBV type. Like other pulsating white dwarf
s, its variability arises from non-radial gravity wave
pulsations within itself. GD 358 was discovered during the 1958–1970 Lowell Observatory
survey for high proper motion
stars in the Northern Hemisphere
. Although it did not have high proper motion, it was noticed that it was a very blue star, and hence might be a white dwarf
. Greenstein
confirmed this in 1969.
In 1968, Arlo U. Landolt
discovered the first intrinsically variable
white dwarf
when he found that HL Tau 76
varied in brightness with a period of approximately 749.5 seconds, or 12.5 minutes. 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
-dominated atmospheres. In 1982, calculations by D. E. Winget and his coworkers suggested that helium-atmosphere DB white dwarfs with surface temperatures around 19,000 K should also pulsate., p. L67. Winget then searched for such stars and found that GD 358 was a variable DB, or DBV, white dwarf. This was the first prediction of a class of variable stars before their observation., p. 89. In 1985, this star was given the variable-star designation V777 Her, which is also another name for this class of variable stars.; , p. 3525
Variable star
A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
of the DBV type. Like other pulsating white dwarf
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 spectral type DA, pp. 891, 895; DBV, or V777 Her,...
s, its variability arises from non-radial gravity wave
Gravity wave
In fluid dynamics, gravity waves are waves generated in a fluid medium or at the interface between two media which has the restoring force of gravity or buoyancy....
pulsations within itself. GD 358 was discovered during the 1958–1970 Lowell Observatory
Lowell Observatory
Lowell Observatory is an astronomical observatory in Flagstaff, Arizona. Lowell Observatory was established in 1894, placing it among the oldest observatories in the United States, and was designated a National Historic Landmark in 1965....
survey for high proper motion
Proper motion
The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...
stars in the Northern Hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
. Although it did not have high proper motion, it was noticed that it was a very blue star, and hence might be a white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
. Greenstein
Jesse L. Greenstein
Jesse Leonard Greenstein was an American astronomer. His parents were Maurice G. and Leah Feingold....
confirmed this in 1969.
In 1968, Arlo U. Landolt
Arlo U. Landolt
Arlo U. Landolt is an American astronomer. Landolt has worked principally in photometry and has published a number of widely used lists of standard stars. In 1995, he received the George van Biesbroeck Prize from the American Astronomical Society...
discovered the first intrinsically variable
Variable star
A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
when he found that HL Tau 76
HL Tau 76
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...
varied in brightness with a period of approximately 749.5 seconds, or 12.5 minutes. 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
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
-dominated atmospheres. In 1982, calculations by D. E. Winget and his coworkers suggested that helium-atmosphere DB white dwarfs with surface temperatures around 19,000 K should also pulsate., p. L67. Winget then searched for such stars and found that GD 358 was a variable DB, or DBV, white dwarf. This was the first prediction of a class of variable stars before their observation., p. 89. In 1985, this star was given the variable-star designation V777 Her, which is also another name for this class of variable stars.; , p. 3525