Whole Earth Telescope

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Whole Earth Telescope
AbbreviationWET [1]
Founder R. Edward Nather
Don E. Winget
Founded at Austin, Texas
FieldsAstronomy
Website www.physics.udel.edu/gp/darc/wet/

The Whole Earth Telescope is an international network of astronomers that collaborate to study variable stars. The distribution of the observatories in longitude allow the selected targets to be continuously monitored despite the rotation of the Earth. [2]

Contents

History

McDonald Observatory of the University of Texas at Austin is a participating site in the WET program McDonald Observatory 82 & 107-inch Telescopes.JPG
McDonald Observatory of the University of Texas at Austin is a participating site in the WET program

This concept was devised by American astronomers R. Edward Nather and Don E. Winget of the University of Texas at Austin. [4] The consortium consists of individual astronomers interested in collaborating to study targets designated by a principal investigator. Where colleagues are not available, astronomers are dispatched to sites that allow telescope time to visitors. [5] Initial funding for WET came from a grant by the US National Science Foundation, which lasted through 1998. [6]

For each site, an observing run begins when the sky is dark, and continues until stopped by weather or dawn. A photometer is used to observe the target object, a nearby comparison star, and the background sky. The data is then sent to the control center. Each site in turn takes up an overlapping observation run, so the result is, ideally, a continuous sequence of data that can then be processed. [7] After constructing a light curve, the data is subject to a Fourier transform to obtain the frequencies of pulsation. [8] Referred to as an XCov, [9] the typical observing run with the WET lasts from 10 to 14 days, and is scheduled for once or twice a year. [7]

The first observation run took place in March, 1988, and it included the Multiple Mirror Telescope in the US, a 1.8 m aperture telescope at the South African Astronomical Observatory, and the IUE observatory in orbit around the Earth. The first target for the run was the star PG 1346+082, or CR Boötis, [10] an AM CVn star. The second target was V803 Centauri, a cataclysmic binary. [11] The campaign was able to monitor the star systems for a continual period of 15 days from six participating sites. [9]

The early focus of the program was the study of pulsating white dwarfs. [7] Most such stars exhibiting non-radial pulsations have multiple pulsation modes, with some having frequencies on the order of a cycle per day. The only way to observe these extended frequencies is continually over durations longer than 24 hours. [12] The observations of PG 1159-035 with the WET, reported in 1991, initiated the study of white dwarf seismology, [13] later termed asteroseismology. By 1998, WET runs had been performed on pulsating white dwarfs of the DOV, DBV, and DAV types, Delta Scuti variables, a rapidly oscillating Ap star, and cataclysmic variables. [8] A total of 16 XCov runs had been completed by May 1998, often covering more than one target per run. Only one failure was reported, for the roAp star HD 166473. [8]

Mt. Cuba Observatory in Delaware is the current headquarters for WET operations Mount Cuba Astronomical Observatory.jpg
Mt. Cuba Observatory in Delaware is the current headquarters for WET operations

Operations for WET moved to Iowa State University in 1995 when the International Institute for Theoretical and Applied Physics offered to help fund the WET program. [6] In 2004, the governing council of WET agreed to study private funding for its operations. This resulted in the formation of the Delaware Astroseismic Research Center (DARC) the following year, and WET operations were moved from Iowa to Delaware. The first run supported by DARC was XCONV25 during May 2006. Operations are supported by the Mount Cuba Astronomical Observatory and the University of Delaware. [4]

The ability to collect photometric data over a long period is vulnerable to weather conditions, the need to allocate time for each telescope, and the situation of each participating astronomer. It was recognized that satellites could accomplish the same task with fewer issues, but at a far higher cost. The MOST spacecraft, launched in 2003, was an early effort to pursue this application. It was able to monitor individual stars for periods of up to 30 days, but was limited to a visual magnitude of 6 or brighter. The Kepler space telescope was launched in 2009 and was able to observe some stars continuously for up to four years. As of 2021, the TESS satellite is performing asteroseismology down to magnitude 17. [14]

Related Research Articles

<span class="mw-page-title-main">Variable star</span> Star whose brightness fluctuates, as seen from Earth

A variable star is a star whose brightness as seen from Earth changes systematically 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:

<span class="mw-page-title-main">Asteroseismology</span> Study of oscillations in stars

Asteroseismology 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 local speed of sound, which in turn depends on local temperature and chemical composition. Because the resulting oscillation modes are sensitive to different parts of the star, they inform astronomers about the internal structure of the star, which is otherwise not directly possible from overall properties like brightness and surface temperature.

<span class="mw-page-title-main">BPM 37093</span> White dwarf star in the constellation Centaurus

BPM 37093 is a variable white dwarf star of the DAV, or ZZ Ceti, type, with a hydrogen atmosphere and an unusually high mass of approximately 1.1 times the Sun's. It is 48 light-years from Earth in the constellation Centaurus and vibrates; these pulsations cause its luminosity to vary. Like other white dwarfs, BPM 37093 is thought to be composed primarily of carbon and oxygen, which are created by thermonuclear fusion of helium nuclei in the triple-alpha process.

<span class="mw-page-title-main">Crab Pulsar</span> Pulsar in the constellation Taurus

The Crab Pulsar is a relatively young neutron star. The star is the central star in the Crab Nebula, a remnant of the supernova SN 1054, which was widely observed on Earth in the year 1054. Discovered in 1968, the pulsar was the first to be connected with a supernova remnant.

<span class="mw-page-title-main">Gamma Pegasi</span> Variable B-type star in the constellation Pegasus

Gamma Pegasi is a star in the constellation of Pegasus, located at the southeast corner of the asterism known as the Great Square. It has the formal name Algenib ; the Bayer designation Gamma Pegasi is Latinized from γ Pegasi and abbreviated Gamma Peg or γ Peg. The average apparent visual magnitude of +2.84 makes this the fourth-brightest star in the constellation. The distance to this star has been measured using the parallax technique, yielding a value of roughly 470 light-years.

Beta Cephei variables, also known as Beta Canis Majoris stars, are variable stars that exhibit small rapid variations in their brightness due to pulsations of the stars' surfaces, thought due to the unusual properties of iron at temperatures of 200,000 K in their interiors. These stars are usually hot blue-white stars of spectral class B and should not be confused with Cepheid variables, which are named after Delta Cephei and are luminous supergiant stars.

<span class="mw-page-title-main">G 29-38</span> White dwarf which undergoes characteristic variability

Giclas 29-38, also known as ZZ Piscium, is a variable white dwarf star of the DAV 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. 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.

<span class="mw-page-title-main">IK Pegasi</span> Star in the constellation Pegasus

IK Pegasi is a binary star system in the constellation Pegasus. It is just luminous enough to be seen with the unaided eye, at a distance of about 154 light years from the Solar System.

<span class="mw-page-title-main">HL Tau 76</span> Star in the constellation Taurus

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.

<span class="mw-page-title-main">G 117-B15A</span> Nearby white dwarf star in the constellation Leo Minor

G117-B15A is a small, well-observed variable white dwarf star of the DAV, or ZZ Ceti, type in the constellation of Leo Minor.

<span class="mw-page-title-main">PG 1159-035</span> Star in the constellation Virgo

PG 1159-035 is the prototypical PG 1159 star after which the class of PG 1159 stars was named. It was discovered in the Palomar-Green survey of ultraviolet-excess stellar objects and, like the other PG 1159 stars, is in transition between being the central star of a planetary nebula and being a white dwarf.

A PG 1159 star, often also called a pre-degenerate, is a star with a hydrogen-deficient atmosphere that is in transition between being the central star of a planetary nebula and being a hot white dwarf. These stars are hot, with surface temperatures between 75,000 K and 200,000 K, and are characterized by atmospheres with little hydrogen and absorption lines for helium, carbon and oxygen. Their surface gravity is typically between 104 and 106 meters per second squared. Some PG 1159 stars are still fusing helium., § 2.1.1, 2.1.2, Table 2. The PG 1159 stars are named after their prototype, PG 1159-035. This star, found in the Palomar-Green survey of ultraviolet-excess stellar objects, was the first PG 1159 star discovered.

<span class="mw-page-title-main">GD 358</span> Star in the constellation Hercules

GD 358 is a variable white dwarf star of the DBV type. Like other pulsating white dwarfs, its variability arises from non-radial gravity wave pulsations within the star 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.

<span class="mw-page-title-main">Ed Nather</span> American astronomer

Roy Edward Nather was an American astronomer, who at the time of his death, was professor emeritus in Astronomy at University of Texas at Austin. He pioneered the fields of asteroseismology of white dwarfs, and observational studies of interacting binary collapsed stars.

<span class="mw-page-title-main">Subdwarf B star</span> Subdwarf star with spectral type B - extremely hot small star

A B-type subdwarf (sdB) is a kind of subdwarf star with spectral type B. They differ from the typical subdwarf by being much hotter and brighter. They are situated at the "extreme horizontal branch" of the Hertzsprung–Russell diagram. Masses of these stars are around 0.5 solar masses, and they contain only about 1% hydrogen, with the rest being helium. Their radius is from 0.15 to 0.25 solar radii, and their surface temperature is from 20,000 to 40,000 K.

<span class="mw-page-title-main">Time-domain astronomy</span> Study of how astronomical objects change with time

Time-domain astronomy is the study of how astronomical objects change with time. Though the study may be said to begin with Galileo's Letters on Sunspots, the term now refers especially to variable objects beyond the Solar System. Changes over time may be due to movements or changes in the object itself. Common targets included are supernovae, pulsating stars, novas, flare stars, blazars and active galactic nuclei. Visible light time domain studies include OGLE, HAT-South, PanSTARRS, SkyMapper, ASAS, WASP, CRTS, GOTO and in a near future the LSST at the Vera C. Rubin Observatory.

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.

<span class="mw-page-title-main">NY Virginis</span> Binary star in the constellation Virgo

NY Virginis is a binary star about 1,940 light-years away. The primary belongs to the rare class of subdwarf B stars, being former red giants with their hydrogen envelope completely stripped by a stellar companion. The companion is a red dwarf star. The binary nature of NY Virginis was first identified in 1998, and the extremely short orbital period of 0.101016 d, together with brightness variability on the timescale of 200 seconds was noticed, resulting in the identification of the primary star as a B-type subdwarf in 2003. Under a proposed classification scheme for hot subdwarfs it would be class sdB1VII:He1. This non-standard system indicates that it is a "normal" luminosity for a hot subdwarf and that the spectrum is dominated by hydrogen rather than helium.

<span class="mw-page-title-main">FG Virginis</span> Variable star in the constellation Virgo

FG Virginis is a well-studied variable star in the equatorial constellation of Virgo. It is a dim star, near the lower limit of visibility to the naked eye, with an apparent visual magnitude that ranges from 6.53 down to 6.58. The star is located at a distance of 273.5 light years from the Sun based on parallax measurements, and is drifting further away with a radial velocity of +16 km/s. Because of its position near the ecliptic, it is subject to lunar occultations.

References

  1. ↑ Heck, Andre (2004), StarBriefs Plus: A Dictionary of Abbreviations, Acronyms and Symbols in Astronomy and Related Space Sciences, Springer Netherlands, p. 1062, ISBN   9780306486036.
  2. ↑ Hogan, Hank (March–April 1989), "The Heavens are Telling", Alcade, vol. 77, no. 4, UT Austin Alumni, p. 22.
  3. 1 2 Bryant, Tracey (May 2009), "World's observatories watching 'cool' star", UDaily, University of Delaware, retrieved 2022-07-20.
  4. 1 2 Provencal, J. L.; et al. (June 2007), "The Delaware Asteroseismic Research Center: Convection in Pulsating White Dwarfs", Communications in Astroseismology, 150: 293, Bibcode:2007CoAst.150..293P, doi: 10.1553/cia150s293 .
  5. ↑ Nather, R. E. (January 1993), "Musings on the whole earth telescope", Baltic Astronomy, 2 (3–4), Bibcode:1993BaltA...2..371N, doi: 10.1515/astro-1993-3-405 .
  6. 1 2 Nather, R. E. (1995), "Status of the Wet", Baltic Astronomy, 4 (2): 117–126, Bibcode:1995BaltA...4..117N, doi: 10.1515/astro-1995-0207 .
  7. 1 2 3 Nather, R. E.; et al. (September 1990), "The Whole Earth Telescope: A New Astronomical Instrument", The Astrophysical Journal, 361: 309, Bibcode:1990ApJ...361..309N, doi:10.1086/169196.
  8. 1 2 3 Winget, D. E. (March 1998), "Ten Years of Science: Lessons on Target Selection for the Whole Earth Telescope", Baltic Astronomy, 7: 3–9, Bibcode:1998BaltA...7....3W, doi: 10.1515/astro-1998-0106 .
  9. 1 2 Provencal, J. L.; et al. (May 1997), "Whole Earth Telescope Observations of the Helium Interacting Binary PG 1346+082 (CR Bootis)", The Astrophysical Journal, 480 (1): 383–394, Bibcode:1997ApJ...480..383P, doi:10.1086/303971, hdl: 10183/108834 .
  10. ↑ Nather, R. Edward (1989), "The Whole Earth Telescope" (PDF), IAU Colloq. 114: White Dwarfs, Lecture Notes in Physics, vol. 328, pp. 109–114, Bibcode:1989LNP...328..109N, doi:10.1007/3-540-51031-1_298, ISBN   978-3-540-51031-4 , retrieved 2022-06-30.
  11. ↑ Kleinman, S. J. (1999), "10 years of the Whole Earth Telescope in 15 minutes or less", 11th European Workshop on White Dwarfs, Bibcode:1999ASPC..169...71K.
  12. ↑ Kawaler, S. D. (1995), "Probing the Extraordinary Ends of Ordinary Stars: White Dwarf Seismology with the Whole Earth Telescope", IAU Colloq. 155: Astrophysical Applications of Stellar Pulsation, arXiv: astro-ph/9503060 , Bibcode:1995ASPC...83...81K.
  13. ↑ Clemens, J. C. (1995), "Perspectives of the Whole Earth Telescope science", Baltic Astronomy, Bibcode:1995BaltA...4..142C, doi: 10.1515/astro-1995-0211 .
  14. ↑ Bradley, Paul A. (December 2021), "How gaps in time-series data affect asteroseismic interpretation", Frontiers in Astronomy and Space Sciences, 8, Bibcode:2021FrASS...8..229B, doi: 10.3389/fspas.2021.793930 , 229.

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