An INFRARED NEBULA ASSOCIATED WITH Δ CEPHEI: EVIDENCE OF MASS LOSS?

Marengo, Massimo; Evans, Nancy Remage; Barmby, P.; Matthews, L. D.; Bono, G.; Welch, D. L.; Romaniello, M.; Huelsman, D.; Su, K. Y. L.; Fazio, G. G.

doi:10.1088/0004-637x/725/2/2392

Cited by 58 publications

(75 citation statements)

References 64 publications

(84 reference statements)

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“…Neilson et al (2010) found that angular diameters measured using the IRSB techniques may be overestimated because of circumstellar media that cause an infrared (IR) excess. This IR excess is presumably caused by mass-loss activity, evidence for which has been found recently on δ Cephei (Marengo et al 2010;Matthews et al 2012). In particular, the K-band flux excess for δ Cephei is 1.5% (Mérand et al 2006), which translates into a difference of ΔK = 0.016 mag.…”

Section: Angular Diameters For δ Cepheimentioning

confidence: 62%

Calibrating the projection factor for Galactic Cepheids

Ngeow

Neilson

Nardetto

et al. 2012

A&A

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Context. The projection factor (p), which converts the radial velocity to pulsational velocity, is an important parameter in the Baade-Wesselink (BW) type analysis and distance scale work. The p-factor is either adopted as a constant or linearly depending on the logarithmic of pulsating periods. Aims. The aim of this work is to calibrate the p-factor if a Cepheid has both the BW distance and an independent distance measurement, and examine the p-factor for δ Cephei -the prototype of classical Cepheids. Methods. We calibrated the p-factor for several Galactic Cepheids that have both the latest BW distances and independent distances either from Hipparcos parallaxes or main-sequence fitting distances to Cepheid-hosted stellar clusters. Results. Based on 25 Cepheids, the calibrated p-factor relation is consistent with latest p-factor relation in literature. The calibrated p-factor relation also indicates that this relation may not be linear and may exhibit an intrinsic scatter. We also examined the discrepancy of empirical p-factors for δ Cephei, and found that the reasons for this discrepancy include the disagreement of angular diameters, the treatment of radial velocity data, and the phase interval adopted during the fitting procedure. Finally, we investigated the impact of the input p-factor in two BW methodologies for δ Cephei, and found that different p-factors can be adopted in these BW methodologies and yet result in the same angular diameters.

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Section: Angular Diameters For δ Cepheimentioning

confidence: 62%

Calibrating the projection factor for Galactic Cepheids

Ngeow

Neilson

Nardetto

et al. 2012

A&A

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“…Instead, the position of RS Pup in the nebula appears essentially coincidental, thus providing a natural explanation to the scarcity of similar Cepheid-nebula associations. Although bow shocks have been observed by Marengo et al (2010) in the δ Cep system, and infrared excess has been identified by Barmby et al (2011) in several Cepheids, the nature of the envelope of RS Pup appears fundamentally different, both in extension and total mass. Another consequence is that the dusty nebula is not a good candidate to resolve a possible evolutionary vs. pulsational mass discrepancy for RS Pup (see e.g.…”

Section: Resultsmentioning

confidence: 99%

The long-period Galactic Cepheid RS Puppis

Kervella¹,

Mérand²,

Szabados³

et al. 2012

A&A

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Context. The southern long-period Cepheid RS Pup is surrounded by a large circumstellar dusty nebula reflecting the light from the central star. Due to the changing luminosity of the central source, light echoes propagate into the nebula. This remarkable phenomenon was the subject of Paper I. The origin and physical properties of the nebula are however uncertain: it may have been created through mass loss from the star itself, or it could be the remnant of a pre-existing interstellar cloud. Aims. Our goal is to determine the three-dimensional structure of the light-scattering nebula, and estimate its mass. This will bring us new clues on the origin of the nebula. Knowing the geometrical shape of the nebula will also allow us to retrieve the distance of RS Pup in an unambiguous manner using a model of its light echoes (in a forthcoming work). Methods. The scattering angle of the Cepheid light in the circumstellar nebula can be recovered from its degree of linear polarization. We thus observed the nebula surrounding RS Pup using the polarimetric imaging mode of the VLT/FORS instrument, and obtained a map of the degree and position angle of linear polarization. Results. From our FORS observations, we derive a three-dimensional map of the distribution of the dust around RS Pup, whose overall geometry is an irregular and geometrically thin layer. The nebula does not present a well-defined central symmetry. Using a simple scattering model, we derive a total dust mass of M dust = 2.9 ± 0.9 M for the light-scattering dust within 1.8 of the Cepheid. This translates into a total mass of M gas+dust = 290 ± 120 M , assuming a dust-to-gas ratio of M dust /M gas = 1.0 ± 0.3%. Conclusions. The high mass of the dusty nebula excludes that it was created by mass-loss from the star. However, the thinness of the dust distribution is an indication that the Cepheid participated to the shaping of the nebula, e.g. through its radiation pressure or stellar wind. RS Pup therefore appears as a regular long-period Cepheid located in an exceptionally dense interstellar environment.

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“…The case of δ Cep was extensively discussed in Marengo et al (2010b). From IRAS observations, Deasy (1988) also detected IR excesses and estimated mass-loss rate ranging from 10 −10 to 10 −6 M yr −1 .…”

Section: Discussionmentioning

confidence: 99%

“…Therefore, the formation of carbon grains in the vicinity of these stars is highly unprobable. The polycyclic aromatic hydrocarbons (PAHs) detected around some Cepheids by Spitzer/IRAC and MIPS have an interstellar origin and result from a density enhancement at the interface between the wind and the interstellar medium that leads to a bow shock (Marengo et al 2010b). It is noteworthy that no signature of PAHs is observed in the MIDI spectrum or the MIDI visibilities (see Figs.…”

Section: Visibility and Spectral Energy Distributionmentioning

confidence: 99%

Extended envelopes around Galactic Cepheids

Gallenne

Mérand

Kervella

et al. 2013

A&A

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Aims. We study the close environment of nearby Cepheids using high spatial resolution observations in the mid-infrared with the VLTI/MIDI instrument, a two-beam interferometric recombiner. Methods. We obtained spectra and visibilities for the classical Cepheids X Sgr and T Mon. We fitted the MIDI measurements, supplemented by B, V, J, H, K literature photometry, with the numerical transfer code DUSTY to determine the dust shell parameters. We used a typical dust composition for circumstellar environments. Results. We detect an extended dusty environment in the spectra and visibilities for both stars, although T Mon might suffer from thermal background contamination. We attribute this to the presence of a circumstellar envelope (CSE) surrounding the Cepheids. This is optically thin for X Sgr (τ 0.55 µm = 0.008), while it appears to be thicker for T Mon (τ 0.55 µm = 0.15). They are located at about 15−20 stellar radii. Following our previous work, we derived a likely period-excess relation in the VISIR PAH1 filter, f 8.6 µm [%]= 0.81(±0.04)P[day]. We argue that the impact of CSEs on the mid-IR period-luminosity (P−L) relation cannot be negligible because they can bias the Cepheid brightness by up to about 30%. For the K-band P−L relation, the CSE contribution seems to be lower (<5%), but the sample needs to be enlarged to firmly conclude that the impact of the CSEs is negligible in this band.

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An INFRARED NEBULA ASSOCIATED WITH Δ CEPHEI: EVIDENCE OF MASS LOSS?

Cited by 58 publications

References 64 publications

Calibrating the projection factor for Galactic Cepheids

Calibrating the projection factor for Galactic Cepheids

The long-period Galactic Cepheid RS Puppis

Extended envelopes around Galactic Cepheids

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