| 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: 47.248mas/yr[2] Dec.: −22.103mas/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 |
| Periastronepoch (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 abinary star[5] system in the northernconstellation ofPegasus. It is a well-studied[11]SX Phoenicis variable star with a brightness that ranges from anapparent 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 thenaked 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 apopulation II star system.[13]
The variability of this star was first reported by Otto Morgenroth in 1934,[5] and the firstlight 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 inspectral 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] aDelta Scuti variable. However, some astronomers classed it as a short-periodRRs 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 withSX Phoenicis had been found, with both showing comparable drifts in their beat periods.[21] Application of theBaade-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 preliminaryorbital period of52.5±0.3 years with aneccentricity of0.77±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 to0.173 M☉, which suggests the companion may be abrown dwarf.[14]
A 2020 analysis of data collected by theAAVSO found three independent frequencies in the variability of the visible component. The primary and secondary modes areradial 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 lowmetallicity.[5] Thestellar 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 awhite dwarf companion as it passed through theasymptotic 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±0.1dex, approaching solar in composition. (This notation indicates thebase-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 amplitudeDelta Scuti variable. The short period of this variable rules it out as anRR 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 themain sequence at the red (cool) edge of theinstability strip.[9] However, it has also been treated as a possible RR Lyrae variable which would be ahorizontal branch star.[8] As an old low-metallicity SX Phoenicis variable, it is very similar toblue stragglers, which are formed from stellar mergers or mass transfer in binary systems.[9]
