Convection, granulation, and period jitter in classical Cepheids

Neilson, Hilding R.; Ignace, Richard

doi:10.1051/0004-6361/201423444

Cited by 29 publications

(19 citation statements)

References 31 publications

(43 reference statements)

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“…It is worth noting that the scatter between the subsequent data points can be intrinsic to the stellar pulsation: this phenomenon is interpreted as a cycleto-cycle jitter in the pulsation period, as observed in V1154 Cyg, the only Cepheid in the original Kepler field (Derekas et al 2012). It was proposed by Neilson & Ignace (2014) that the physical mechanism underlying the period jitter of V1154 Cyg is linked to the presence of convective hot spots on the photosphere of the star. This explanation may also apply to RS Pup, whose relatively low effective temperature could favor the appearance of such convective features.…”

Section: Phasing Of the Datasetsmentioning

confidence: 97%

Observational calibration of the projection factor of Cepheids

Kervella

Trahin

Bond

et al. 2017

A&A

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The projection factor (p-factor) is an essential component of the classical Baade-Wesselink (BW) technique, which is commonly used to determine the distances to pulsating stars. It is a multiplicative parameter used to convert radial velocities into pulsational velocities. As the BW distances are linearly proportional to the p-factor, its accurate calibration for Cepheids is of critical importance for the reliability of their distance scale. We focus on the observational determination of the p-factor of the long-period Cepheid RS Pup (P = 41.5 days). This star is particularly important as this is one of the brightest Cepheids in the Galaxy and an analog of the Cepheids used to determine extragalactic distances. An accurate distance of 1910 ± 80 pc (±4.2%) has recently been determined for RS Pup using the light echoes propagating in its circumstellar nebula. We combine this distance with new VLTI/PIONIER interferometric angular diameters, photometry, and radial velocities to derive the p-factor of RS Pup using the code Spectro-Photo-Interferometry of Pulsating Stars (SPIPS). We obtain p = 1.250 ± 0.064 (±5.1%), defined for cross-correlation radial velocities. Together with measurements from the literature, the p-factor of RS Pup confirms the good agreement of a constant p = 1.293 ± 0.039 (±3.0%) model with the observations. We conclude that the p-factor of Cepheids is constant or mildly variable over a broad range of periods (3.7 to 41.5 days).

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Section: Phasing Of the Datasetsmentioning

confidence: 97%

Observational calibration of the projection factor of Cepheids

Kervella

Trahin

Bond

et al. 2017

A&A

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“…The origin of modulated variability in Cepheids is currently largely unclear, although different mechanisms that have been suggested may be related, such as strange-mode and non-radial pulsations, magnetic cycles, or granulation (Buchler et al 1997;Buchler & Kolláth 2001;Kovtyukh et al 2003;Stothers 2009;Neilson & Ignace 2014). As mentioned in A14, the very different timescale of RV curve modulation found in long and short-period Cepheids suggests that multiple mechanisms may be at play.…”

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confidence: 99%

Discovery of cycle-to-cycle modulated spectral line variability and velocity gradients in long-period Cepheids

Anderson

2016

Mon. Not. R. Astron. Soc.

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This work reports the discovery of cycle-to-cycle modulated spectral line and atmospheric velocity gradient variability in long-period Cepheids based on 925 high-resolution optical spectra of Carinae (P ∼ 35.5 d) recorded during three heavy duty-cycle monitoring campaigns (in 2014, 2015, and 2016). Spectral line variability is investigated via crosscorrelation functions (CCFs) computed using three sets of spectral lines (weak, solar, strong). A metallic line velocity gradient, δv r (t), is computed as the difference between weak and strong-line RVs. CCF shape indicators BIS (asymmetry), FWHM, and depth all exhibit clear phase-dependent variability patterns that differ from one pulsation cycle to the next. Weakline CCFs exhibit these effects more clearly than strong-line CCFs. BIS exhibits the most peculiar modulated variability and can be used to identify the presence of cycle-to-cycle modulated line profile variations. δv r (t) clearly exhibits cycle-to-cycle differences that correlate very closely with modulated BIS variability, suggesting perturbations of the atmospheric velocity field as the cause for modulated spectral line variability. These perturbations are most significant during contraction and are not in phase with the pulsation, transmitting information between consecutive pulsation cycles. This work shows RV curve modulation to be a consequence of atmospheric velocity gradient perturbations. Possible origins of these perturbations and their impact on Cepheid RV measurements as well as the projection factor used in Baade-Wesselink-type distance determinations are discussed.

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“…These new surveys will shed new light to our understanding of variable objects and related astrophysics. Furthermore, as these surveys continuously monitor variable stars, we can measure changes in periods and instabilities (Turner et al 2006;Smith 2013;Neilson et al 2012;Neilson & Ignace 2014).…”

Section: Introductionmentioning

confidence: 99%

Kmtnet Supernova Program Variable Objects I. NGC 2784 Field

He¹,

Neilson²,

Lee³

et al. 2016

Journal of The Korean Astronomical Society

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We present analyses of ∼1250 variable sources identified in a 20 square degree field toward NGC 2784 by the KMTNet Supernova Program. We categorize the variable sources into three groups based on their B-band variability. The first group consists of 31 high variability sources with their Bband RMS variability greater than 0.3 magnitudes. The second group of medium variability contains 265 sources with RMS variability between 0.05 and 0.3 magnitudes. The remaining 951 sources belong to the third group of low variability with an RMS variability smaller than 0.05 magnitudes. Of the entire ∼1250 sources, 4 clearly show periods of variability greater than 100 days, while the rest have periods shorter than ∼51 days or no reliable periods. The majority of the sources show either rather irregular variability or short periods faster than 2 days. Most of the sources with reliable period determination between 2 and 51 days belong to the low-variability group, although a few belong to the medium-variability group. All the variable sources with periods longer than 35 days appear to be very red with B − V > 1.5 and V − I > 2.1 magnitudes. We classify candidates of 51 Cepheids, 17 semi-regular variables, 3 Mira types, 2 RV(B) Tauri stars, 26 eclipsing binary systems and 1 active galactic nucleus. The majority of long-term variables in our sample belong to either Mira or semi-regular types, indicating that long-term variability may be more prominent in post-main sequence phases of late-type stars. The depth of the eclipsing dips of the 26 candidates for eclipsing binaries is equivalent to ∼0.61 as the average relative size of the two stars in the binary system. Our results illustrate the power of the KMTNet Supernova Program for future studies of variable objects.

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Convection, granulation, and period jitter in classical Cepheids

Cited by 29 publications

References 31 publications

Observational calibration of the projection factor of Cepheids

Observational calibration of the projection factor of Cepheids

Discovery of cycle-to-cycle modulated spectral line variability and velocity gradients in long-period Cepheids

Kmtnet Supernova Program Variable Objects I. NGC 2784 Field

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