DY Pegasi

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DY Pegasi
DYPegLightCurve.png
A visual band light curve DY Pegasi, plotted from ASAS-SN data [1]
Observation data
Epoch J2000       Equinox J2000
Constellation Pegasus
Right ascension 23h 08m 51.186s [2]
Declination +17° 12′ 56.00″ [2]
Apparent magnitude  (V)9.95 – 10.62 [3]
Characteristics
Spectral type A3 to F1 [4]
Variable type SX Phe [5] [3]
Astrometry
Radial velocity (Rv)−25.30±2.7 [6]  km/s
Proper motion (μ)RA: 47.248  mas/yr [2]
Dec.: −22.103  mas/yr [2]
Parallax (π)2.4588 ± 0.0452  mas [2]
Distance 1,330 ± 20  ly
(407 ± 7  pc)
Absolute magnitude  (MV)2.34 [7]
0.84 [8]
Orbit [5]
Period (P)15,425.0±205.7 d
Semi-major axis (a)≥ 0.254±0.034  AU
Eccentricity (e)0.65 ± 0.10
Periastron epoch (T)2438276.86149 ± 0.00013 HJD
Details
Mass 1.54 M☉ [7]
1.40 [8]   M☉
Radius 2.09±0.25 R☉ [4]
3.74 – 3.95 [8]   R☉
Luminosity 11.34+2.82
−2.51 L☉ [4]
34.6±2.1 [8]   L☉
Temperature 7,660 K [7] (7,950 – 6,750) [9]   K
Metallicity [Fe/H]−0.56 [5]   dex
Rotational velocity (v sin i)23.6 [5]  km/s
Age 1.7 [7]   Gyr
Other designations
DY Peg, BD+16°4877, HD  218549, HIP  114290 [10]
Database references
SIMBAD data

DY Pegasi, abbreviated DY Peg, is a binary star [5] system in the northern constellation of Pegasus. It is a well-studied [11] SX Phoenicis variable star with a brightness that ranges from an apparent visual magnitude of 9.95 down to 10.62 with a period of 1.75 hours. [3] This system is much too faint to be seen with the naked eye, but can be viewed with large binoculars or a telescope. [12] Based on its high space motion and low abundances of heavier elements, it is a population II star system. [13]

Contents

Observation history

The variability of this star was first reported by Otto Morgenroth in 1934, [5] and the first light curves of its photometric behavior were constructed by A. V. Soloviev in 1938. [14] This curve showed a rapid increase of 0.7 in magnitude followed by a slower decline. [15] It was found to be an intrinsic variable with an "ultra-short" period of 105 minutes. The 'b-v' color index of the star was found to vary with each cycle, corresponding to a change in spectral type from A7 at maximum to F1 at minimum. Direct observation of spectra showed a variation from A3 to A9. [16] Evidence was found of small variations in the light curve between each cycle. [17]

By 1972, it was widely regarded as a dwarf cepheid; [18] a Delta Scuti variable. However, some astronomers classed it as a short-period RRs Lyrae variable. [19] Photometric observations of DY Peg in 1975 by E. H. Geyer and M. Hoffman showed non-periodic changes to the light curve that suggested an overtone pulsation. [20] A frequency analysis of observations made by A. Masani and P. Broglia in 1953 strengthened the evidence that DY Peg is a double mode cepheid, showing a fundamental pulsation and a weaker first overtone with a period ratio of 0.764. [17] By 1982, similarities with SX Phoenicis had been found, with both showing comparable drifts in their beat periods. [21] Application of the Baade-Wesselink method provided a preliminary distance estimate to DY Peg of 820 ly (250 pc). [9]

In 2003, J. N. Fu and C. Sterken suggested that much of the long-term trend in variability period changes could be explained by a highly-eccentric orbital model, although it was not deemed a complete solution since some small residuals remained from the period 1930–1950. They computed a preliminary orbital period of 52.5±0.3 years with an eccentricity of 0.77±0.01. [22] L.-J. Li and S.-B. Qian in 2010 found a mass estimate of the secondary in the range of 0.028 to 0.173  M☉ , which suggests the companion may be a brown dwarf. [14]

Properties

A 2020 analysis of data collected by the AAVSO found three independent frequencies in the variability of the visible component. The primary and secondary modes are radial pulsations with 13.71249 and 17.7000 cycles per day, respectively, while a newly discovered non-radial mode has a frequency of 18.138 cycles per day. Consistent with being a population II star, it has a low metallicity. [5] The stellar class ranges from A3 to F1 over each cycle, [4] and the radius of the star varies by 3.5%. [4] To explain certain discrepant properties of the system, H.-F. Xue and J.-S. Niu proposed that the primary may be accreting mass from an orbiting dust disk. This is conjectured to be leftover material from a white dwarf companion as it passed through the asymptotic giant branch. [5]

DY Pegasi has been classified as a SX Phoenicis variable on the basis of its low metallicity. However, a 2014 study by S. Barcza and J. M. Benkő found a much higher general abundance of heavy elements with [M/H] = −0.05±0.1 dex, approaching solar in composition. (This notation indicates the base-10 logarithm of the ratio of "metals" 'M' to hydrogen 'H', compared to the same abundances in the Sun. A value of 0.0 is solar.) They proposed that this may instead be a high amplitude Delta Scuti variable. The short period of this variable rules it out as an RR Lyrae variable. [8]

The properties of DY Pegasi are uncertain due to the presence of an unknown companion, but it appears to lie close to the main sequence at the red (cool) edge of the instability strip. [9] However, it has also been treated as a possible RR Lyrae variable which would be a horizontal branch star. [8] As an old low-metallicity SX Phoenicis variable, it is very similar to blue stragglers, which are formed from stellar mergers or mass transfer in binary systems. [9]

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 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">Cepheid variable</span> Type of variable star that pulsates radially

A Cepheid variable is a type of variable star that pulsates radially, varying in both diameter and temperature. It changes in brightness, with a well-defined stable period and amplitude.

<span class="mw-page-title-main">RR Lyrae variable</span> Type of variable star

RR Lyrae variables are periodic variable stars, commonly found in globular clusters. They are used as standard candles to measure (extra) galactic distances, assisting with the cosmic distance ladder. This class is named after the prototype and brightest example, RR Lyrae.

<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 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">Delta Scuti variable</span> Subclass of young pulsating star

A Delta Scuti variable is a subclass of young pulsating star. These variables as well as classical cepheids 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. The variables follow a period-luminosity relation in certain passbands like other standard candles such as Cepheids. 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. One last sub-class are the pre-main sequence (PMS) Delta Scuti variables.

<span class="mw-page-title-main">Instability strip</span> Region of an astronomical diagram

The unqualified term instability strip usually refers to a region of the Hertzsprung–Russell diagram largely occupied by several related classes of pulsating variable stars: Delta Scuti variables, SX Phoenicis variables, and rapidly oscillating Ap stars (roAps) near the main sequence; RR Lyrae variables where it intersects the horizontal branch; and the Cepheid variables where it crosses the supergiants.

<span class="mw-page-title-main">Stellar pulsation</span>

Stellar pulsations are caused by expansions and contractions in the outer layers as a star seeks to maintain equilibrium. These fluctuations in stellar radius cause corresponding changes in the luminosity of the star. Astronomers are able to deduce this mechanism by measuring the spectrum and observing the Doppler effect. Many intrinsic variable stars that pulsate with large amplitudes, such as the classical Cepheids, RR Lyrae stars and large-amplitude Delta Scuti stars show regular light curves.

<span class="mw-page-title-main">SX Phoenicis variable</span>

An SX Phoenicis variable is a type of variable star. These stars exhibit a short period pulsation behavior that varies on time scales of 0.03–0.08 days. They have spectral classifications in the range A2-F5 and vary in magnitude by up to 0.7. Compared to the Sun, these stars have a lower metallicity, which means they have a reduced abundance of elements other than hydrogen and helium. They also have relatively high space velocity and low luminosities for stars of their stellar classification. These properties distinguish the SX Phoenicis variables from their cousins, the Delta Scuti variables. The latter have longer periods, higher metallicity and large amplitudes.

<span class="mw-page-title-main">SX Phoenicis</span>

SX Phoenicis is a variable star in the southern constellation Phoenix. With an apparent visual magnitude ranging around 7.33, it is too faint to be readily seen with the naked eye and requires binoculars. It is located 272 light years from the Sun, as determined from an annual parallax shift of 12 mas.

<span class="mw-page-title-main">BL Boötis</span> Star in the constellation Boötes

BL Boötis is a pulsating star in the constellation Boötes. It is the prototype of a class of anomalous Cepheids which is intermediate in the H-R diagram between the type I classical Cepheids and the type II Cepheids.

<span class="mw-page-title-main">V473 Lyrae</span> Star in the constellation Lyra

V473 Lyrae is a variable star in the constellation Lyra. It is an unusual Classical Cepheid variable with a visual range of 5.99 to 6.35.

<span class="mw-page-title-main">AC Andromedae</span> Variable star in the constellation Andromeda

AC Andromedae is a variable star in the constellation Andromeda. Its maximum apparent visual magnitude is 10.77, but can be seen fainter down to a magnitude of 11.9.

<span class="mw-page-title-main">SZ Tauri</span> Variable star in Taurus

SZ Tauri is a variable star in the equatorial constellation of Taurus. The brightness of this star varies from an apparent visual magnitude of 6.39 down to 6.69 with a period of 3.149 days, which is near the lower limit of visibility to the naked eye. The distance to this star is approximately 2,070 light years based on parallax measurements. There is some indication this may be a binary system, but the evidence is inconclusive.

<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.

<span class="mw-page-title-main">EU Tauri</span> Variable star in the constellation Taurus

EU Tauri is a variable star in the equatorial constellation of Taurus. With a brightness that cycles around an apparent visual magnitude of 8.07, it is too faint to be visible to the naked eye. The distance to this star is approximately 3,900 light years based on parallax measurements, but it is drifting closer with a radial velocity of −2.5 km/s. The position of this star near the ecliptic means it is subject to lunar occultations.

<span class="mw-page-title-main">SZ Lyncis</span> Variable star in the constellation of Lynx

SZ Lyncis is a binary star system in the northern constellation of Lynx, abbreviated SZ Lyn. It is a variable star with an apparent visual magnitude that fluctuates around 9.58, which is too faint to be visible to the naked eye. The distance to this system is approximately 1,700 light years based on parallax measurements, and it is drifting further away with a radial velocity of 34 km/s.

<span class="mw-page-title-main">AI Velorum</span> Variable star in the constellation of Lynx

AI Velorum is a variable star in the southern constellation of Vela, abbreviated AI Vel. It is a prototype for a class of high amplitude Delta Scuti variables. The apparent visual magnitude of this star fluctuates around 6.56, which is just bright enough to be dimly visible to the naked eye. The distance to AI Vel is approximately 327 light years based on parallax measurements, and it is drifting further away with a radial velocity of about 9 km/s.

<span class="mw-page-title-main">BL Herculis</span> Variable star in the constellation Hercules

BL Herculis is a variable star in the northern constellation of Hercules. Its apparent visual magnitude ranges from 9.70 to 10.62, so it is never bright enough to be seen with the naked eye, even with ideal observing conditions. Its distance from the Sun is about 3,850 light-years, and it is moving away from us at 18 km/sec. It is the prototype of the BL Herculis class of variable star, a short-period subset of the pulsating Cepheid variables.

<span class="mw-page-title-main">AE Ursae Majoris</span> Variable star in the constellation Ursa Major

AE Ursae Majoris is a star in the northern circumpolar constellation of Ursa Major, abbreviated AE UMa. It is a variable star that ranges in brightness from a peak apparent visual magnitude of 10.86 down to 11.52. The distance to this star is approximately 2,400 light years based on parallax measurements.

<span class="mw-page-title-main">VZ Cancri</span> Variable star in the constellation Cancer

VZ Cancri is a variable star in the constellation Cancer, abbreviated VZ Cnc. It varies in brightness with a period of 0.178364 days, from an apparent visual magnitude of 7.18 down to 7.91, which lies below the typical threshold of visibility for the naked eye. The distance to this star is approximately 724 light years based on parallax measurements, and it is receding from the Sun with a radial velocity of 25 km/s.

References

  1. ↑ "ASAS-SN Variable Stars Database". ASAS-SN Variable Stars Database. ASAS-SN. Retrieved 6 January 2022.
  2. 1 2 3 4 5 Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics . 649: A1. arXiv: 2012.01533 . Bibcode:2021A&A...649A...1G. doi: 10.1051/0004-6361/202039657 . S2CID   227254300. (Erratum:  doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  3. 1 2 3 Samus', N. N; et al. (2017), "General catalogue of variable stars: Version GCVS 5.1", Astronomy Reports, 61 (1): 80, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID   125853869.
  4. 1 2 3 4 5 Wilson, W. J. F.; et al. (April 1998), "Studies of Large-Amplitude delta Scuti Variables. III. DY Pegasi", The Publications of the Astronomical Society of the Pacific, 110 (746): 433–450, Bibcode:1998PASP..110..433W, doi: 10.1086/316148 .
  5. 1 2 3 4 5 6 7 8 Xue, Hui-Fang; Niu, Jia-Shu (November 2020), "DY Pegasi: An SX Phoenicis Star in a Binary System with an Evolved Companion", The Astrophysical Journal, 904 (1): 12, arXiv: 2008.02542 , Bibcode:2020ApJ...904....5X, doi: 10.3847/1538-4357/abbc12 , S2CID   221006143, 5.
  6. ↑ Gontcharov, G. A. (November 2006), "Pulkovo Compilation of Radial Velocities for 35495 Hipparcos stars in a common system", Astronomy Letters, 32 (11): 759–771, arXiv: 1606.08053 , Bibcode:2006AstL...32..759G, doi:10.1134/S1063773706110065, S2CID   119231169.
  7. 1 2 3 4 Hintz, Eric G.; et al. (June 2004), "Period Changes in the SX Phoenicis Star DY Pegasi", The Publications of the Astronomical Society of the Pacific, 116 (820): 543–553, Bibcode:2004PASP..116..543H, doi: 10.1086/420858 , S2CID   120366195.
  8. 1 2 3 4 5 6 Barcza, S.; Benkő, J. M. (August 2014), "Fundamental parameters of RR Lyrae stars from multicolour photometry and Kurucz atmospheric models - III. SW And, DH Peg, CU Com and DY Peg", Monthly Notices of the Royal Astronomical Society, 442 (2): 1863–1876, arXiv: 1405.4184 , Bibcode:2014MNRAS.442.1863B, doi: 10.1093/mnras/stu978 .
  9. 1 2 3 4 Meylan, G.; et al. (April 1986), "RR Lyrae, delta Scuti, SX Phoenicis stars and Baade-Wesselink method. I. Photometric and radial velocity measurements of four field stars: RR Cet, DX Del, BS AQR and DY Peg", Astronomy and Astrophysics, 159: 261–268, Bibcode:1986A&A...159..261B.
  10. ↑ "DY Peg". SIMBAD . Centre de données astronomiques de Strasbourg . Retrieved 2020-01-02.
  11. ↑ Fu, J. N.; et al. (March 2009), "Pulsations and Period Changes of the SX Phoenicis Star DY Pegasi", Publications of the Astronomical Society of the Pacific, 121 (877): 251, Bibcode:2009PASP..121..251F, doi: 10.1086/597829 .
  12. ↑ "The astronomical magnitude scale", International Comet Quarterly, retrieved 2020-12-31.
  13. ↑ Frolov, M. S.; Irkaev, B. N. (January 1984), "On the SX Phe-Type Stars", Information Bulletin on Variable Stars, 2462: 1, Bibcode:1984IBVS.2462....1F.
  14. 1 2 Li, L. -J.; Qian, S. -B. (June 2010), "A Period Investigation of the SX Phoenicis Star DY Pegasi", The Astronomical Journal, 139 (6): 2639–2642, Bibcode:2010AJ....139.2639L, doi: 10.1088/0004-6256/139/6/2639 .
  15. ↑ Iriarte, Braulio (September 1952), "A Photoelectric Light-Curve of DY Peg", Astrophysical Journal, 116: 382, Bibcode:1952ApJ...116..382I, doi: 10.1086/145621 .
  16. ↑ Geilker, Chas. D. (July 1957), "Three-color photometry of the ultrashort-period variable DY Pegasi.", Astronomical Journal, 62: 143, Bibcode:1957AJ.....62..143G, doi: 10.1086/107494 .
  17. 1 2 Kozar, T. (August 1980), "DY Pegasi - a Double Mode Dwarf Cepheid?", Information Bulletin on Variable Stars, 1834: 1, Bibcode:1980IBVS.1834....1K.
  18. ↑ Warner, B.; Nather, R. E. (1972), "Three-colour photometry of DY Pegasi", Monthly Notices of the Royal Astronomical Society, 156 (3): 315, Bibcode:1972MNRAS.156..315W, doi: 10.1093/mnras/156.3.315 .
  19. ↑ Geyer, E. H.; Hoffmann, M. (October 1974), "Maxima of the RRs-variables CY Aqr, DY Her and DY Peg", Information Bulletin on Variable Stars, 936: 1, Bibcode:1974IBVS..936....1G.
  20. ↑ Geyer, E. H.; Hoffmann, M. (August 1975), "A two-colour photometry of the short period RR Lyrae star DY Peg.", Astronomy & Astrophysics Supplement Series, 21: 183–188, Bibcode:1975A&AS...21..183G.
  21. ↑ Coates, D. W.; et al. (April 1982), "The rates of change of the fundamental and overtone periods of SX Phe", Monthly Notices of the Royal Astronomical Society, 199: 135–139, Bibcode:1982MNRAS.199..135C, doi: 10.1093/mnras/199.1.135 .
  22. ↑ Fu, J. N.; Sterken, C. (July 2003), "Long-term variability of the SX Phoenicis star CY Aquarii", Astronomy and Astrophysics, 405 (2): 685–688, Bibcode:2003A&A...405..685F, doi: 10.1051/0004-6361:20030589 .
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