GD 356

Last updated
GD 356
Observation data
Epoch J2000.0        Equinox J2000.0
Constellation Draco
Right ascension 16h 40m 57.16s [1]
Declination +53° 41′ 09.6″ [1]
Apparent magnitude  (V)15.06 [1]
Characteristics
Spectral type DC7 [1]
Apparent magnitude  (B)~15.39 [1]
Apparent magnitude  (V)~15.06 [1]
Apparent magnitude  (R)~15.1 [1]
Apparent magnitude  (I)~14.0 [1]
Apparent magnitude  (J)~14.493 [1]
Apparent magnitude  (H)~14.479 [1]
Apparent magnitude  (K)~14.369 [1]
U−B color index -0.52 [1]
B−V color index +0.33 [1]
Variable type 0.2% over 115 minutes
Astrometry
Radial velocity (Rv)25 km/s
Proper motion (μ)RA: -0.125 [2]   mas/yr
Dec.: -0.200 [2]   mas/yr
Parallax (π)545.4 [1]  ± 3.5  mas
Distance 65  ly
(21.1  pc)
Absolute magnitude  (MV)13.43
Details
Mass 0.67  M☉
Surface gravity (log g)8  cgs
Temperature 7510  K
Rotation 115 minutes
Age About 2.1  Gyr
Other designations
Gliese  1205, LP  137-43, EGGR 329, WD 1639+537
Database references
SIMBAD data
ARICNS data

GD 356 is a white dwarf in the constellation of Draco showing an unusual emission of circular polarised light. The star is 65 light years from earth. [3] The class of this white dwarf is DAe meaning that it has a cool helium rich atmosphere. [4] This star exhibits emission lines showing the Zeeman effect in the hydrogen Balmer spectrum. [4] GD 356 belongs to a class of high field magnetic white dwarfs (HFMWD), but it is unique in that the split lines are purely emission lines with no absorption. The emission region appears to be due to a heated upper layer in the photosphere in which the magnetic field is uniform to within 10%. [4] The emission can be produced by an atmosphere at 7500K in a gravity field of 106 ms−2 and a magnetic field of 13 megaGauss. The magnetically split emission lines, Hα and Hβ, are circularly polarised. [5] One explanation is that it is caused by a large electric current flowing between the poles of the star and a highly conducting planet. [3] Other explanations such as being due to Bondi-Hoyle accretion or due to a corona are ruled out by the lack of radio and X-ray emissions. Accretion of gas at a low rate over a broad area of the star, only results in heating at levels high in the atmosphere and not down to the opacity depth of 1.0 as observed with these lines.

Contents

The spectrum does not vary over periods of hours or days. This indicates that the rotation axis must match the magnetic dipole axis. The power radiated by the emission lines is 1027 erg s−1. Overall light from the white dwarf varies by 0.2% smoothly over a period of 117 minutes. [4] Explanations given for the variation are a dark spot rotating with the star. This could be near the rotation pole when viewed nearly edge on, or could be on the equator with the pole pointing roughly towards Earth. [6]

Other catalog names for this are LP 137-43, EGGR 329 and WD 1639+537. [5]

Properties

The mass of GD 356 is 0.67 M☉ whereas when it was a main sequence star it would have had a mass of 3.25 M☉. In order to reach a temperature of 7510 K it would have become a white dwarf about 1.6 Gya. Prior to this the main sequence lifetime would have been 500 million years giving it a total age of 2.1 billion years. [4] The current magnitude is 15. [7]

The absolute visual magnitude is +13.43±0.16. Proper motion is 0.24" pa, in direction 212°. [5] The trigonometric parallax is 21.1 parsecs. Tangential motion is 25 km−1. [7]

Spectrum

The Hα line splitting is 44.5 nm. In similar white dwarfs an absorption line is expected to be seen instead, so that means the emission has sufficient energy to overpower any absorption. [7] The emission was originally discovered by Jesse L. Greenstein. [7] The original Hα line has a wavelength at 655.2 nm and is called the π component. The blue shifted component σ− has wavelength 633.4 nm and red shifted component line σ+ is at 678.2 nm. [7]

Possible companion

The unipolar-inductor theory says that a high-conduction companion orbits. As it moves through the star's magnetic field, a high voltage is produced between the star facing side of the planet and the dark side. A current then flows along field lines to the point on the star where the field lines meet the star's photosphere, the current is completed through the photosphere heating it up. [4]

A planet in a close orbit would develop the shape of the Roche potential and is very likely to be molten due to tidal heating. [4] A planet with a density of over five g/cm3 is stable at an orbital period longer than 4.7 hours. A planet in this kind of orbit may have a temperature of 560 K and could be detectable in infrared if it was large enough. [4]

Infrared observations rule out a large companion such as a brown dwarf or other large planet over twelve Jupiter masses. This is based on the expected temperature of 2.1 billion year old planets. [4]

A planet could possibly get into this situation by evaporating while orbiting inside the gaseous shell of the red giant and at the same time having its orbit decay due to bow-shock friction with the gas. Tides induce on the expanded star by the planet would also cause the orbit to decay, rather than expand as might have been expected to loss of gas from the star. These possibilities have been studied because that is the expected future of the Earth. Another hypothesis is that close-in planets could have formed during the merger of two white dwarfs. [4]

Related Research Articles

<span class="mw-page-title-main">Stellar corona</span> Outermost layer of a stars atmosphere

A corona is the outermost layer of a star's atmosphere. It consists of plasma.

<span class="mw-page-title-main">White dwarf</span> Type of stellar remnant composed mostly of electron-degenerate matter

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 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.

<span class="mw-page-title-main">X-ray astronomy</span> Branch of astronomy that uses X-ray observation

X-ray astronomy is an observational branch of astronomy which deals with the study of X-ray observation and detection from astronomical objects. X-radiation is absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and satellites. X-ray astronomy uses a type of space telescope that can see x-ray radiation which standard optical telescopes, such as the Mauna Kea Observatories, cannot.

<span class="mw-page-title-main">Brown dwarf</span> Type of substellar object larger than a planet

Brown dwarfs 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 massive gas giant planets and the least massive stars, approximately 13 to 80 times that of Jupiter (MJ). However, they can fuse deuterium (2H) and the most massive ones can fuse lithium (7Li).

<span class="mw-page-title-main">Chromosphere</span> Layer in the Suns atmosphere above the photosphere

A chromosphere is the second layer of a star's atmosphere, located above the photosphere and below the solar transition region and corona. The term usually refers to the Sun's chromosphere, but not exclusively.

<span class="mw-page-title-main">Wolf 359</span> Red dwarf in the constellation Leo

Wolf 359 is a red dwarf star located in the constellation Leo, near the ecliptic. At a distance of approximately 7.9 light years from Earth, it has an apparent magnitude of 13.54 and can only be seen with a large telescope. Wolf 359 is one of the nearest stars to the Sun; only the Alpha Centauri system, Barnard's Star, and the brown dwarfs Luhman 16 and WISE 0855−0714 are known to be closer. Its proximity to Earth has led to its mention in several works of fiction.

<span class="mw-page-title-main">Exomoon</span> Moon beyond the Solar System

An exomoon or extrasolar moon is a natural satellite that orbits an exoplanet or other non-stellar extrasolar body.

<span class="mw-page-title-main">RS Canum Venaticorum variable</span>

An RS Canum Venaticorum variable is a type of variable star. The variable type consists of close binary stars having active chromospheres which can cause large stellar spots. These spots are believed to cause variations in their observed luminosity. Systems can exhibit variations on timescales of years due to variation in the spot surface coverage fraction, as well as periodic variations which are, in general, close to the orbital period of the binary system. Some systems exhibit variations in luminosity due to their being eclipsing binaries. Typical brightness fluctuation is around 0.2 magnitudes. They take their name from the star RS Canum Venaticorum.

Z Andromedae is a binary star system consisting of a red giant and a white dwarf. It is the prototype of a type of cataclysmic variable star known as symbiotic variable stars or simply Z Andromedae variables. The brightness of those stars vary over time, showing a quiescent, more stable phase and then an active one with a more pronounced variability and stronger brightening and/or dimming.

GRW +70 8247 is a white dwarf star located 42 light-years from Earth in the constellation Draco. With a magnitude of about 13 it is visible only through a large telescope.

An AM Canum Venaticorum star, is a rare type of cataclysmic variable star named after their type star, AM Canum Venaticorum. In these hot blue binary variables, a white dwarf accretes hydrogen-poor matter from a compact companion star.

HIP 70849 is a star with two non-stellar companions in the southern constellation Lupus. It is a 10th magnitude star, making it too faint to be visible to the naked eye. The system is located at a distance of 78.7 light-years from the Sun based on parallax measurements.

HD 81817 is a possible binary star system with two brown dwarf companions in the northern circumpolar constellation of Draco. It has an orange hue and is visible to the naked eye with an apparent visual magnitude of 4.28. The system is located at a distance of approximately 990 light years from the Sun based on parallax, and is drifting closer with a radial velocity of −7 km/s. It is a member of the IC 2391 moving group.

<span class="mw-page-title-main">CE Gruis</span> Binary star system in the constellation Grus

CE Gruis is a faint binary star system in the constellation Grus. It is a variable star, with a B-band brightness that ranges from a peak magnitude of 17.4 down to a minimum of 19.5 over a period of 108.6 minutes. The system is composed of a white dwarf and donor star, locked into a close, synchronous orbit. In such systems, known as polars, material from the donor star does not form an accretion disc around the white dwarf because of its intense magnetic field, but rather streams directly onto it along columns.

SW Sextantis variable stars are a kind of cataclysmic variable star; they are double-star systems in which there is mass transfer from a red dwarf to a white dwarf forming a stable accretion disc around the latter. Unlike other non-magnetic cataclysmic variables, the emission lines from hydrogen and helium are not doubled, except briefly near phase 0.5.

<span class="mw-page-title-main">V392 Persei</span> Nova in the constellation Perseus

V392 Persei, also known as Nova Persei 2018, is a bright nova in the constellation Perseus discovered on April 29, 2018. It was previously known as a dwarf nova.

<span class="mw-page-title-main">WD 0145+234</span> White dwarf in the constellation Aries

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.

<span class="mw-page-title-main">WD J0914+1914</span> White dwarf star in the constellation Cancer

WD J0914+1914 is the first single white dwarf star found to have a giant planet orbiting it. Evidence of the giant planet was discovered by a team of astronomers from the UK, Chile and Germany.

<span class="mw-page-title-main">UZ Fornacis</span> Binary star system in the constellation Fornax

UZ Fornacis is a binary star in the constellation of Fornax. It appears exceedingly faint with a maximum apparent magnitude 17.0. Its distance, as measured by Gaia using the parallax method, is about 780 light-years.

<span class="mw-page-title-main">BG Canis Minoris</span> Variable star in the constellation of Canis Minor

BG Canis Minoris is a binary star system in the equatorial constellation of Canis Minor, abbreviated BG CMi. With an apparent visual magnitude that fluctuates around 14.5, it is much too faint to be visible to the naked eye. Parallax measurements provide a distance estimate of approximately 2,910 light years from the Sun.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 "SIMBAD Query Result: GD 356". SIMBAD. Centre de Données astronomiques de Strasbourg . Retrieved 13 June 2012.
  2. 1 2 "ARI Data Base for Nearby Stars". ARICNS. Centre of Astronomy, Heidelberg University.
  3. 1 2 Muir, Hazel (1 August 1998). "The Earth could be in for an electrifying time". New Scientist (2145): 7.
  4. 1 2 3 4 5 6 7 8 9 10 Wickramasinghe, Dayal T.; Farihi, Jay; Tout, Christopher A.; Ferrario, Lilia; Stancliffe, Richard J. (9 February 2010). "Does GD356 have a Terrestrial Planetary Companion?". Monthly Notices of the Royal Astronomical Society . 404 (4): 1984–1991. arXiv: 1002.1761 . Bibcode:2010MNRAS.404.1984W. doi:10.1111/j.1365-2966.2010.16417.x. S2CID   119255099.
  5. 1 2 3 Ferrario, Lilia; Wickramasinghe, Dayal T.; Liebert, James; Schmidt, Gary D.; Bieging, John H. (1997). "The Magnetic Field and Emission-Line Spectrum of the Remarkable White Dwarf GD 356". Monthly Notices of the Royal Astronomical Society. 289 (1): 105–116. Bibcode:1997MNRAS.289..105F. doi: 10.1093/mnras/289.1.105 .
  6. ↑ Brinkworth, C. S.; M. R. Burleigh; G. A. Wynn; T. R. Marsh (2004). "Photometric variability of the unique magnetic white dwarf GD 356". Monthly Notices of the Royal Astronomical Society. 384 (3): L33–L37. arXiv: astro-ph/0312311 . Bibcode:2004MNRAS.348L..33B. doi:10.1111/j.1365-2966.2004.07538.x. S2CID   15677179.
  7. 1 2 3 4 5 Greenstein, Jesse L.; James K. McCarthy (15 February 1985). "Emission lines in the magnetic white dwarf GD 356". Astrophysical Journal, Part 1. 289: 732–747. Bibcode:1985ApJ...289..732G. doi:10.1086/162937. ISSN   0004-637X.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.