Delta Scuti variable

A Delta Scuti variable (sometimes termed dwarf cepheid) is a variable star which exhibits variations in its luminosity due to both radial and non-radial pulsations of the star's surface. The variables are important standard candles and have been used to establish the distance to the Large Magellanic Cloud, globular clusters, open clusters, and the Galactic Center.[1][2][3][4] The variables follow a period-luminosity relation in certain passbands like other standard candles such as Cepheids.[3][4][5][6] SX Phoenicis variables are generally considered to be a subclass of Delta Scuti variables that contain old stars, and can be found in globular clusters. SX Phe variables also follow a period-luminosity relation.[3][6] The recently discovered Rapidly oscillating Ap stars are also a subclass of Delta Scuti variables, found on the main sequence.[7] One last sub-class are the pre-main sequence (PMS) Delta Scuti variables.

The OGLE and MACHO surveys have detected nearly 3000 Delta Scuti variables in the Large Magellanic Cloud.[5][8] Typical brightness fluctuations are from 0.003 to 0.9 magnitudes in V over a period of a few hours, although the amplitude and period of the fluctuations can vary greatly. The stars are usually A0 to F5 type giant or main sequence stars. The high-amplitude Delta Scuti variables are also called AI Velorum stars. They are the second most abundant variable source in the Milky Way after white dwarfs.

Delta Scuti stars exhibit both radial and non-radial luminosity pulsations. Non-radial pulsations are when some parts of the surface move inwards and some outward at the same time. Radial pulsations are a special case, where the star expands and contracts around its equilibrium state by altering the radius to maintain its spherical shape. The variations are due to the swelling and shrinking of the star through the Eddington Valve (or Kappa) Mechanism. The stars have a helium rich atmosphere. As helium is heated it becomes more ionised, which is more opaque. So at the dimmest part in the cycle the star has highly ionised opaque helium in its atmosphere blocking part of the light from escaping. The energy from this “blocked light” causes the helium to heat up, expand, ionise, become more transparent and therefore allow more light through. As more light is let through the star appears brighter and, with the expansion, the helium begins to cool down. Hence the helium contracts and heats up again and the cyclical process continues. Throughout their lifetime Delta Scuti stars exhibit pulsation when they are situated on the classical Cepheid instability strip. They then move across from the main sequence into the giant branch.

The prototype of these sorts of variable stars is Delta Scuti (δ Sct), which exhibits brightness fluctuations from +4.60 to +4.79 in apparent magnitude with a period of 4.65 hours. Other well known Delta Scuti variables include Altair, Denebola (β Leonis) and β Cassiopeiae. Vega (α Lyrae) is a suspected Delta Scuti variable,[9] but this remains unconfirmed.

Examples

Designation (name) Constellation Discovery Apparent magnitude (Maximum)[10] Apparent magnitude (Minimum)[10] Range of magnitude Period Spectral type Comment
Gamma Boötis Boötes 3m.02 3m.07 0.05 6.96 h A7III
Epsilon Cephei Cepheus 4m.15 4m.21 0.06 0.98 h F0IV
Delta Scuti Scutum 4m.6 4m.79 0.19 4.65 h F2 IIIp prototype

References

  1. ^ McNamara, D. H.; Madsen, J. B.; Barnes, J.; Ericksen, B. F. (2000). The Distance to the Galactic Center, PASP
  2. ^ McNamara, D. Harold; Clementini, Gisella; Marconi, Marcella (2007). The Distance to the Galactic Center, AJ
  3. ^ a b c Majaess, D. J.; Turner, D. G.; Lane, D. J.; Henden, A. A.; Krajci, T. (2011). Anchoring the Universal Distance Scale Via a Wesenheit Template, Journal of the American Association of Variable Star Observers
  4. ^ a b Majaess, D. J.; Turner, D. G.; Lane, D. J.; Krajci, T. (2011). Deep Infrared ZAMS Fits to Benchmark Open Clusters Hosting Delta Scuti Stars, Journal of the American Association of Variable Star Observers
  5. ^ a b Poleski, R.; Soszyñski, I.; Udalski, A.; Szymañski, M. K.; Kubiak, M.; Pietrzyñski, G.; Wyrzykowski, Ł.; Szewczyk, O.; Ulaczyk, K. (2010). The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. VI. Delta Scuti Stars in the Large Magellanic Cloud, Acta Astronomica
  6. ^ a b Cohen, Roger E.; Sarajedini, Ata (2012). SX Phoenicis period-luminosity relations and the blue straggler connection, MNRAS
  7. ^ Kopacki, G.; Kołaczkowski, Z.; Pigulski, A. (2003). Variable stars in the globular cluster M 13, Acta Astronomica
  8. ^ Garg, A.; Cook, K. H.; Nikolaev, S.; Huber, M. E.; Rest, A.; Becker, A. C.; Challis, P.; Clocchiatti, A.; Miknaitis, G.; Minniti, D.; Morelli, L.; Olsen, K.; Prieto, J. L.; Suntzeff, N. B.; Welch, D. L.; Wood-Vasey, W. M. (2010). High-amplitude δ-Scutis in the Large Magellanic Cloud, AJ
  9. ^ I.A., Vasil'yev; et al. (1989-03-17), On the Variability of Vega, Commission 27 of the I.A.U, retrieved 2007-10-30
  10. ^ a b (visual magnitude, unless marked (B) (= blue) or (p) (= photographic))
18 Vulpeculae

18 Vulpeculae is a binary star system in the northern constellation of Vulpecula, located about 489 light years away from the Sun. It is visible to the naked eye as a faint, white-hued star with a combined apparent visual magnitude of 5.51. The system is moving closer to the Earth with a heliocentric radial velocity of −11.7 km/s.This is a double-lined spectroscopic binary system with an orbital period of 9.3 days and a small eccentricity of 0.0116. It is a detached binary with a semimajor axis of 0.14742 ± 0.00047 AU. The system contains a Delta Scuti variable, but the temperature places it to the blue (hotter) side of the δ Scuti instability strip. The combined stellar classification of this system remains unclear, with classes of A3 III, A1 IV, A3 V, and A2 IV being given. The ultraviolet spectrum matches an A3 dwarf star. It shows no spectral peculiarities.

26 Arietis

26 Arietis is a variable star in the northern constellation of Aries. 26 Arietis is the Flamsteed designation; it also bears the variable star designation UU Arietis. The apparent visual magnitude of this star is 6.14, which, according to the Bortle Dark-Sky Scale, is within the naked eye visibility limit in dark rural skies. The annual parallax shift of 13.78 mas is equivalent to a distance of approximately 215 light-years (66 parsecs) from Earth. The star is receding from the Earth with a heliocentric radial velocity of +15 km/s.This is an A-type main sequence star with a stellar classification of A9 V. It is a Delta Scuti variable with a variability period of 0.0676 days and an amplitude of 0.010 in magnitude. The star is around a billion years old with 1.74 times the mass of the Sun and 2.32 times the Sun's radius. The star is radiating 15 times the luminosity of the Sun from its photosphere at an effective temperature of 7,430 K.

28 Andromedae

28 Andromedae (abbreviated 28 And) is a Delta Scuti variable star in the constellation Andromeda. 28 Andromedae is the Flamsteed designation. It also bears the variable star name GN Andromedae. Its apparent magnitude is 5.214, with long-term variability of luminosity variations.28 Andromedae is an A-type giant star, meaning it is colored bluish-white. Parallax estimates made by the Hipparcos spacecraft put the star at a distance of about 205 light years (63 parsecs). It's moving towards the solar system at a velocity of 10.30 km/s.

28 Cancri

28 Cancri is a star system in the zodiac constellation of Cancer. It is a variable star with the designation CX Cancri, and is close to the lower limit of visibility with the naked eye, having a mean apparent visual magnitude of 6.05. The annual parallax shift seen from Earth's orbit is 7.32 mas, which provides a distance estimate of about 450 light years. It is moving away from the Sun with a radial velocity of around +9 km/s.Based upon proper motion variation, this is an astrometric binary system with high likelihood (99.8%). The visible component has a stellar classification of F0 Vn, indicating it is a F-type main-sequence star with "nebulous" lines due to rapid rotation. It is a Delta Scuti variable star with a period of 0.0960 days and an amplitude of 0.020 in magnitude. With 2.4 times the mass of the Sun it is spinning with a high projected rotational velocity of 133 km/s. 28 Cancri is radiating roughly 65 times the Sun's luminosity from its photosphere at an effective temperature of around 7,516 K.

38 Arietis

38 Arietis (abbreviated 38 Ari) is a variable star in the northern constellation of Aries. 38 Arietis is the Flamsteed designation. It was once designated 88 Ceti, forming part of the neighboring constellation of Cetus. With an apparent visual magnitude of +5.18, it is bright enough to be viewed with the naked eye. The measured annual parallax shift of 27.52 mas is equivalent to a distance of approximately 119 light-years (36 parsecs) from Earth.

The spectrum of this star matches a stellar classification of A7 III-IV, with the luminosity class of III-IV indicating it shows traits part way between the subgiant and giant star stages of its evolution. It is a Delta Scuti variable with a period of 0.0355 days (51 minutes) and a magnitude change of 0.040. This star is larger than the Sun, with more than double the Sun's radius and 11 times the luminosity. This energy is being radiated into outer space from the atmosphere at an effective temperature of 7,638 K, giving it the white-hued glow of an A-type star.

38 Cancri

38 Cancri is a variable star in the zodiac constellation Cancer, located around 607 light years from the Sun. This object has the variable star designation BT Cancri; 38 Cancri is the Flamsteed designation. It is a member of the Praesepe cluster but is a challenge to view with the naked eye, having an apparent visual magnitude of 6.65. The star is moving closer to the Earth with a heliocentric radial velocity of +32 km/s.This is an evolving subgiant star with a stellar classification of F0 IV. It was found to be a pulsating variable by Michel Breger in 1970 and is classed as a Delta Scuti variable. The star displays a pattern of variation showing up to 22 different frequencies, with three being dominant. The brightness varies by up to 0.07 in magnitude. The star has a magnetic field with a computed longitudinal field strength of −215±149 G. It has 1.8 times the mass of the Sun and 1.8 times the Sun's radius. The star is radiating 59 times the Sun's luminosity from its photosphere at an effective temperature of around 7,300 K.

59 Aurigae

59 Aurigae, often abbreviated as 59 Aur, is a star in the constellation Auriga. Its baseline apparent magnitude is 6.1, meaning it can just barely be seen with the naked eye as a dim, yellow-white hued star. Based on parallax measurements, it is located about 483 light-years (148 parsecs) away from the Sun.This object is a Delta Scuti variable, meaning it varies in luminosity due to pulsations on its surface, ranging in magnitude from 5.94 down to 6.14 with a period of 0.154412 days (3.7 h). For that reason, it has been given the variable star designation OX Aurigae. The star's spectrum matches that of an F-type main-sequence star and it has a spectral type of F2V. It has 2.5 times the mass of the Sun and 5.7 times the Sun's radius. 59 Aurigae is thought to be around 700 million years old, and is radiating 64 times the Sun's luminosity from its photosphere an effective temperature of 6,808 K.

64 Eridani

64 Eridani is a single, yellow-white hued star in the constellation Eridanus with the variable star designation S Eridani. It is a faint star but visible to the naked eye with an apparent visual magnitude of 4.77. The annual parallax shift is measured at 11.24 mas, which provides a distance estimate of about 290 light years. It is moving closer to the Sun with a radial velocity of around −9 km/s.This is an F-type main-sequence star with a stellar classification of F0 V. It is catalogued a low amplitude Delta Scuti variable with a primary period of 0.273 days. Alternatively, it may be an RR Lyrae variable of type 'c'. 64 Eridani is spinning rapidly with a projected rotational velocity of 212 km/s. This is giving the star an oblate shape with an equatorial bulge that is 8% larger than the polar radius. The star is an estimated 644 million years old with 1.5 times the mass of the Sun. It is radiating 80 times the Sun's luminosity from its photosphere at an effective temperature of roughly 7,346 K.

71 Tauri

71 Tauri is a suspected triple star system in the zodiac constellation Taurus, located 146 light years from the Sun. It is visible to the naked eye as a faint, yellow-white hued star with an apparent visual magnitude of +4.48. The star is moving further away from the Earth with a heliocentric radial velocity of +38 km/s. It is a member of the Hyades open cluster.The primary component is an F-type main-sequence star with a stellar classification of F0 V. It is a Delta Scuti variable with an amplitude of 0.02 in magnitude and a frequency of 0.16 d−1. This star has about 1.94 times the mass of the Sun and 3.34 times the Sun's radius. It has a projected rotational velocity of 192 km s−1, for an estimated rotation period of 14.2 days. Extreme ultraviolet flares have been observed coming from this star's hot corona, and it is the second brightest X-ray source in the Hyades.

8 Aquilae

8 Aquilae is a star in the equatorial constellation of Aquila, located 266 light years away from the Sun. 8 Aquilae is the Flamsteed designation. It can be viewed with the naked eye in good seeing conditions, appearing as a dim, yellow-white hued star with an apparent visual magnitude of 6.08. The star is moving further from the Earth with a heliocentric radial velocity of +12 km/s.Abt and Morrell (1995) found a stellar classification of F0 IV for this star, suggesting it is an F-type subgiant. In their 2010 study, Fox Machado et al. assigned a class of F2 III, which matches an evolved giant star. It is a Delta Scuti variable with at least three overlapping pulsation frequencies. The star is nearly a billion years old with a relatively high rotation rate, showing a projected rotational velocity of 105 K. It has 1.6 times the mass of the Sun and is radiating 19 times the Sun's luminosity from its photosphere at an effective temperature of about 7,395 K.

AR Scorpii

AR Scorpii (AR Sco) is a binary pulsar that consists of white dwarf and a red dwarf. It is the first "white dwarf-pulsar" to be discovered. The 3.56-hour period in AR Sco's light curve caused it to be misclassified as a Delta Scuti variable, but in 2016, this period was found to be the binary orbital period. In addition, the system shows very strong optical, ultraviolet, and radio pulsations originating from the red dwarf with a period of just 1.97 minutes, which is a beat period from the orbital rotation and the white dwarf spin. These pulsations occur when a relativistic beam from the white dwarf sweeps across the red dwarf, which then reprocesses the beam into the observed electromagnetic energy. At present, the white dwarf is not accreting significantly, and the system is powered by the spin-down of the white dwarf. The pulsar is about the same size as Earth.

AR Sco's unusual nature was first noticed by amateur astronomers.

AZ Canis Minoris

AZ Canis Minoris is a yellow-white star in the constellation Canis Minor. It is a Delta Scuti variable just visible to the naked eye in good conditions with a maximum visual magnitude of 6.44 and minimum of 6.51, with a period of 2.3 hours. It is around 402 light-years (123 parsecs) distant.

CL Draconis

CL Draconis is a single star in the northern circumpolar constellation of Draco. It can be viewed with the naked eye, having an apparent visual magnitude of 4.96. The distance to this star, as determined from its annual parallax shift of 29.9 mas, is 109 light years. It is moving closer to the Earth with a heliocentric radial velocity of −11 km/s. The star has a relatively high proper motion, traversing the celestial sphere at the rate of 0.185″/yr.Based upon a stellar classification of F0 IV, this is an aging F-type subgiant star that has consumed the hydrogen at its core. It is spinning rapidly with a projected rotational velocity of 165 km/s, giving it an oblate shape with an equatorial bulge that is estimated to be 8% larger than the polar radius. CL Dra is a Delta Scuti variable, changing brightness with an amplitude of 0.010 magnitude over a period of 1.83 hours. CL Dra has 1.68 times the mass of the Sun and is radiating 10.2 times the Sun's luminosity from its photosphere at an effective temperature of 7,439 K.

CP Boötis

CP Boötis is a yellow-white hued star in the northern constellation of Boötes. With a baseline apparent visual magnitude of 6.40, it is at or near the lower limit for visibility with the typical naked eye in good viewing conditions. The distance to this star can be estimated from its annual parallax shift of 12.91 mas, which yields a range of 252.6 light years. It is moving further away with a heliocentric radial velocity of +5.9 km/s.This is an F-type subgiant star with a stellar classification of F8 IVw, which indicates it has nearly consumed the hydrogen at its core and is now evolving into a giant star. It is a low amplitude Delta Scuti variable that varies by 0.02 magnitude. At the age of 1.7 billion years it is spinning with a projected rotational velocity of 5.7 km/s. The star has 1.77 times the mass of the Sun and is radiating 12 times the Sun's luminosity from its photosphere at an effective temperature of 6,276 K.

EW Aquarii

EW Aquarii is a star in the constellation Aquarius. A low amplitude Delta Scuti variable, it varies between magnitudes 6.41 and 6.48 over 2.16 hours. Located around 439 light-years distant, it shines with a luminosity approximately 31 times that of the Sun and has a surface temperature of 7163 K.

GP Andromedae

GP Andromedae (often abbreviated to GP And) is a Delta Scuti variable star in the constellation Andromeda. It is a pulsating star, with its brightness varying with an amplitude of 0.55 magnitudes around a mean magnitude of 10.7.

HD 15082

HD 15082 (also known as WASP-33) is a star located roughly 399 light years away in the northern constellation of Andromeda. The star is a Delta Scuti variable and a planetary transit variable. A hot Jupiter type extrasolar planet, named WASP-33b or HD 15082b, orbits this star with an orbital period of 1.22 days. It is the first Delta Scuti variable known to host a planet.

HD 182475

HD 182475 is a Delta Scuti variable star in the equatorial constellation of Aquila.

Sigma Octantis

Sigma Octantis (σ Octantis, abbreviated Sig Oct, σ Oct), officially named Polaris Australis , is the current South Star. Its position near the southern celestial pole makes it the southern hemisphere's pole star. This is a solitary star in the southern circumpolar constellation of Octans. Located approximately 281 light-years from Earth, it is classified as a giant star with a spectral type of F0 III. Sigma Octantis is a Delta Scuti variable, with its average magnitude of 5.47 varying by about 0.03 magnitudes every 2.33 hours.

Pulsating
Eruptive
Cataclysmic
Rotating
Eclipsing

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