Detection of a Degenerate Companion of the Sx Phoenicis Star Kz Hydrae by Studying Its Long-Term Variability

Fu, Jian-Ning; Khokhuntod, Pongsak; Rodríguez‐López, C.; Boonyarak, Chayan; Marak, Kanokwan; López-González, M. J.; Zhu, L.-Y.; Qian, S.‐B.; Jiang, Shi-Yang

doi:10.1088/0004-6256/135/5/1958

Cited by 11 publications

(7 citation statements)

References 14 publications

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“…The high-amplitude δ Scuti stars (hereafter HADS) are traditionally found with slow rotation, one or two dominant radial modes with amplitudes larger than 0.1 mag, although some of them may have low-amplitude nonradial modes (e.g., Poretti 2003). SX Phoenicis (SX Phe) stars is a subgroup of HADS with low metallicity and large spatial motion (see e.g., Fu et al 2008a). They are old Pop.…”

Section: Introductionmentioning

confidence: 99%

AE Ursae Majoris – a δ Scuti Star in the Hertzsprung Gap

Niu

et al. 2017

Mon. Not. R. Astron. Soc.

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We analyze the photometric data and spectroscopic data that collect on the δ Scuti star AE UMa. The fundamental and the first overtone frequencies are confirmed as f 0 = 11.62560 c d −1 and f 1 = 15.03124 c d −1 , respectively, from the frequency content by analyzing of the 40 nights light curve spanning from 2009 to 2012. Additionally, another 37 frequencies are identified as either the harmonics or the linear combinations of the fundamental and the first overtone frequencies, among which 25 are newly detected. The rate of period change of the fundamental mode is determined as (1/P 0 )(dP 0 /dt) = 5.4(±1.9) × 10 −9 yr −1 as revealed from the O − C diagram based on the 84 newly determined times of maximum light combined with those derived from the literature. The spectroscopic data suggests that AE UMa is a population I δ Scuti star. With these physical properties, we perform theoretical explorations based on the stellar evolution code MESA on this target, considering that the variation of pulsation period is caused by secular evolutionary effects. We finally constraint the AE UMa with the physical parameters as: the mass of 1.805 ± 0.055 M ⊙ , the radius of 1.647 ± 0.032 × 10 11 cm, the luminosity of 1.381 ± 0.048 (log L/L ⊙ ) and the age of 1.055 ± 0.095 × 10 9 yr. AE UMa can be the (Pop. I) δ Scuti star that locates just after the second turn-off of its evolutional track leaving the main sequence, a star in the phase of the Hertzsprung Gap with a helium core and a hydrogen-burning shell.

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Section: Introductionmentioning

confidence: 99%

AE Ursae Majoris – a δ Scuti Star in the Hertzsprung Gap

Niu

et al. 2017

Mon. Not. R. Astron. Soc.

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“…Yang et al (1985) suggested that there is a small amplitude light time effect. The newest research paper of this star was published by Fu et al (2008). The light time effect is confirmed with a much larger amplitude and a longer period.…”

Section: Kz Hyamentioning

confidence: 73%

“…Papers have been published about AD CMi (Khokhuntod et al 2007), DY Her (Boonyarak and Jiang 2007), KZ Hya (Fu et al 2008), DY Peg (Fu et al 2009), andVZ Cnc (Boonyarak et al 2009). In this paper we present (O-C) calculations for 14 HADS (GP And, CY Aqr, BS Aqr, YZ Boo, AD CMi, VZ Cnc, EH Lib, DY Her, V927 Her, KZ Hya, BE Lyn, V1162 Ori, DY Peg, and CW Ser) among our monitoring targets by using all times of light maximum available.…”

Section: Introductionmentioning

confidence: 99%

On the period variations of several low declination high amplitude delta Scuti variables

Boonyarak

Khokhuntod

et al. 2011

Astrophys Space Sci

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A 16-inch Schmidt-Cassegrain telescope on the campus of Naresuan University of Thailand and several similar-size telescopes in China equipped with CCD cameras were used to observe 14 high amplitude delta Scuti stars: GP And, CY Aqr, BS Aqr, YZ Boo, AD CMi, VZ Cnc, EH Lib, DY Her, V927 Her, KZ Hya, BE Lyn, V1162 Ori, DY Peg, and CW Ser, between the years 1999 and 2010. Data were also collected from scientific journals and sources on the Internet for these variable stars. Times of light maximum of these delta Scuti stars were then either determined from the observations or obtained from the literature to analyze the pulsation period variations. For the 14 delta Scuti stars we concluded that 7 stars (BS Aqr, CY Aqr, AD CMi, EH Lib, KZ Hya, BE Lyn and DY Peg) are binary or multiple systems. 10 delta Scuti stars are found with periods increasing with rates between 5.86 × 10 −9 and 2.34 × 10 −6 per year and the other 4 stars (BS Aqr, DY Her, BE Lyn and DY Peg) show periods decreasing with rates of about 10 −9 to 10 −8 per year.

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“…Liu et al (1991) confirm this hypothesis. Fu et al (2008) renewed the binary solution and suggest its unseen companion is a massive white dwarf with mass larger than 0.86 solar mass. Here we try to use a binary evolution model to solve this problem.…”

Section: Introductionmentioning

confidence: 94%

The history of KZ Hya and its unseen companions

Jiang

2008

Proc. IAU

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Abstract. KZ Hya is a short-period high amplitude metal pool population II pulsating variable. Its spectral type is B9-A7 III/IV. Its average effective temperature is 7640K. But its mass is only 0.97 solar mass. From normal stellar evolution and H-R diagram, we can not get such a solar mass star at post main sequence stage with so high effective temperature and so early type spectra. We observe this star since 1984 till now, 23years past. Finally we prove it is inside a binary with at least 2 unseen companions. The most massive companion has mass larger than 0.76 solar mass, mostly may be 0.99 to 3.99 solar mass. That means this companion must be a massive white dwarf. The distance between tow companions is about 10 AU. If the companion is white dwarf, this binary are fairly inside the nebula. This system is very old, older than 7.59 billion years. The nebula should be already diluted to very low density so that we cant see the nebula directly. As its spectra type is B9III/VI at some time of maximum light and the visual absolute magnitude is 2.78, about 2 magnitudes higher than our sun. We can image that at the end of AGB stage of the companion, the strong fast winds from hot central core push away the outer atmosphere of KZ Hya. Later KZ Hya absorbed a part of Helium rich material from the companion. This will cause hydrogen content X decrease from 0.75 to about 0.62. Then KZ Hya looks like a hot post main sequence star

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Detection of a Degenerate Companion of the Sx Phoenicis Star Kz Hydrae by Studying Its Long-Term Variability

Cited by 11 publications

References 14 publications

AE Ursae Majoris – a δ Scuti Star in the Hertzsprung Gap

AE Ursae Majoris – a δ Scuti Star in the Hertzsprung Gap

On the period variations of several low declination high amplitude delta Scuti variables

The history of KZ Hya and its unseen companions

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