Pulsating low-mass white dwarfs in the frame of new evolutionary sequences

Calcaferro, Leila Magdalena; Córsico, Alejandro H.; Althaus, Leandro Gabriel

doi:10.1051/0004-6361/201630376

Cited by 17 publications

(20 citation statements)

References 92 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Then, for the selected modes, the absolute value of the rate of period change for the pre-ELMV mode is two orders of magnitude higher than for the δ Sct model. These results are in agreement with Breger & Pamyatnykh (1998) regarding δ Sct stars, and Calcaferro et al (2017) in connection with pre-ELMV stars. Therefore, the rate of period change is a potential tool with which to distinguish the two kinds of stars.…”

Section: Rate Of Period Changesupporting

confidence: 93%

Comparing the asteroseismic properties of pulsating pre-extremely low mass white dwarf and δ Scuti stars

Arias

Romero

Córsico

et al. 2018

A&A

Self Cite

View full text Add to dashboard Cite

Context. Pulsating extremely low-mass pre-white dwarf stars (pre-ELMV), with masses between ~0.15 M⊙ and ~0.30 M⊙, constitute a new class of variable stars showing g- and possibly p-mode pulsations with periods between 320 and 6000 s (frequencies between 14.4 and 270 c/d), driven by the κ mechanism operating in the second He ionization zone. On the other hand, main sequence δ Scuti stars, with masses between 1.2 and 2.5 M⊙, pulsate in low-order g and p modes with periods in the range [700–28 800] s (frequencies in the range [3–123] c/d), driven by the κ mechanism operating in the He II ionization zone and the turbulent pressure acting in the HI ionization layer. Interestingly enough, the instability strips of pre-ELM white dwarf and δ Scuti stars nearly overlap in the Teff vs. log g diagram, leading to a degeneracy when spectroscopy is the only tool to classify the stars and pulsation periods only are considered. Aims. Pre-ELM white dwarf and δ Scuti stars are in very different stages of evolution and therefore their internal structure is very distinct. This is mirrored in their pulsational behavior, thus employing asteroseismology should allow us to distinguish between these groups of stars despite their similar atmospheric parameters. Methods. We have employed adiabatic and non-adiabatic pulsation spectra for models of pre-ELM white dwarfs and δ Scuti stars, and compare their pulsation periods, period spacings, and rates of period change. Results. Unsurprisingly, we found substantial differences in the period spacing of δ Scuti and pre-ELM white dwarf models. Even when the same period range is observed in both classes of pulsating stars, the modes have distinctive signature in the period spacing and period difference values. For instance, the mean period difference of p-modes of consecutive radial orders for δ Scuti model are at least four times longer than the mean period spacing for the pre-ELM white dwarf model in the period range [2000–4600] s (frequency range [18.78–43.6] c/d). In addition, the rate of period change is two orders of magnitudes larger for the pre-ELM white dwarfs compared to δ Scuti stars. In addition, we also report the discovery of a new variable star, SDSSJ075738.94+144827.50, located in the region of the Teff versus log g diagram where these two kind of stars coexist. Conclusions.The characteristic spacing between modes of consecutive radial orders (p as well as g modes) and the large differences found in the rates of period change for δ Scuti and pre-ELM white dwarf stars suggest that asteroseismology can be employed to discriminate between these two groups of variable stars. Furthermore, we found that SDSSJ075738.94+144827.50 exhibits a period difference between p modes characteristic of a δ Sct star, assuming consecutive radial order for the observed periods.

show abstract

Section: Rate Of Period Changesupporting

confidence: 93%

Comparing the asteroseismic properties of pulsating pre-extremely low mass white dwarf and δ Scuti stars

Arias

Romero

Córsico

et al. 2018

A&A

Self Cite

View full text Add to dashboard Cite

show abstract

“…If the high-gravity-BLAPs are low mass He-core pre-WDs, we might be able to detect a period evolution in the pulsations (Ṗ ; see also Calcaferro et al 2017). Low-mass WDs evolve from a surface gravity of 5.25 to 5.75 and a pulsation period of ≈ 500 sec to ≈ 200 sec in only ≈ 1 Myrs.…”

Section: Discussionmentioning

confidence: 99%

A New Class of Large-amplitude Radial-mode Hot Subdwarf Pulsators

Kupfer

Bauer

Burdge

et al. 2019

ApJL

View full text Add to dashboard Cite

Using high-cadence observations from the Zwicky Transient Facility at low Galactic latitudes, we have discovered a new class of pulsating, hot, compact stars. We have found four candidates, exhibiting blue colors (g −r ≤ −0.1 mag), pulsation amplitudes of > 5%, and pulsation periods of 200−475 sec. Fourier transforms of the lightcurves show only one dominant frequency. Phase-resolved spectroscopy for three objects reveals significant radial velocity, T eff and log(g) variations over the pulsation cycle, consistent with large amplitude radial oscillations. The mean T eff and log(g) for these stars are consistent with hot subdwarf B (sdB) effective temperatures and surface gravities. We calculate evolutionary tracks using MESA and adiabatic pulsations using GYRE for low-mass helium-core pre-white dwarfs and low mass helium-burning stars. Comparison of low-order radial oscillation mode periods with the observed pulsation periods show better agreement with the pre-white dwarf models. Therefore, we suggest that these new pulsators and Blue Large-Amplitude Pulsators (BLAPs) could be members of the same class of pulsators, composed of young ≈ 0.25 − 0.35 M ⊙ helium-core pre-white dwarfs.

show abstract

“…Detection of rapid rotation in SDSS J1604+0627 would also be extremely interesting in the context of a post-merger formation. Continued monitoring of SDSS J1604+0627 will help to reveal the nature of this signal as we may be able to detect the secular rate of period change from pulsations, as explored in (pre-)ELM WD evolutionary models by Calcaferro et al (2017a). Multiwavelength observations can also discern between these explanations, as the characteristic colors of surface inhomogeneities from spots and stellar pulsations can be very different (discussed for WDs by, e.g., Dupuis et al 2000;Robinson et al 1982).…”

Section: Sdss J1604+0627mentioning

confidence: 99%

The McDonald Observatory search for pulsating sdA stars

Bell

Pelisoli²,

Brown

et al. 2018

A&A

View full text Add to dashboard Cite

Context. The nature of the recently identified “sdA” spectroscopic class of stars is not well understood. The thousands of known sdAs have H-dominated spectra, spectroscopic surface gravity values between main sequence stars and isolated white dwarfs, and effective temperatures below the lower limit for He-burning subdwarfs. Most are likely products of binary stellar evolution, whether extremely low-mass white dwarfs and their precursors or blue stragglers in the halo. Aims. Stellar eigenfrequencies revealed through time series photometry of pulsating stars sensitively probe stellar structural properties. The properties of pulsations exhibited by sdA stars would contribute substantially to our developing understanding of this class. Methods. We extend our photometric campaign to discover pulsating extremely low-mass white dwarfs from the McDonald Observatory to target sdA stars classified from SDSS spectra. We also obtain follow-up time series spectroscopy to search for binary signatures from four new pulsators. Results. Out of 23 sdA stars observed, we clearly detect stellar pulsations in 7. Dominant pulsation periods range from 4.6 min to 12.3 h, with most on timescales of approximately one hour. We argue specific classifications for some of the new variables, identifying both compact and likely main sequence dwarf pulsators, along with a candidate low-mass RR Lyrae star. Conclusions. With dominant pulsation periods spanning orders of magnitude, the pulsational evidence supports the emerging narrative that the sdA class consists of multiple stellar populations. Since multiple types of sdA exhibit stellar pulsations, follow-up asteroseismic analysis can be used to probe the precise evolutionary natures and stellar structures of these individual subpopulations.

show abstract

Pulsating low-mass white dwarfs in the frame of new evolutionary sequences

Cited by 17 publications

References 92 publications

Comparing the asteroseismic properties of pulsating pre-extremely low mass white dwarf and δ Scuti stars

Comparing the asteroseismic properties of pulsating pre-extremely low mass white dwarf and δ Scuti stars

A New Class of Large-amplitude Radial-mode Hot Subdwarf Pulsators

The McDonald Observatory search for pulsating sdA stars

Contact Info

Product

Resources

About