Mid‐Infrared Spectroscopy of Carbon Stars in the Small Magellanic Cloud

Sloan, G. C.; Kraemer, K. E.; Matsuura, M.; Wood, P. R.; Price, S. D.; Egan, M. P.

doi:10.1086/504516

Cited by 78 publications

(184 citation statements)

References 53 publications

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“…The theoretical work of Mattsson et al (2008) and Wachter et al (2008) showed that the mass-loss rates of carbon stars may not be sensitive to metallicity. Numerous recent studies using Spitzer spectra of AGB stars in low-metallicity Local Group galaxies (e.g., Sloan et al 2006;Zijlstra et al 2006;Lagadec et al 2007;Matsuura et al 2007;Sloan et al 2008) seem to support this claim. Similar results were obtained by Groenewegen et al (2007), who found in their modeling of the IRS spectra of 60 carbon stars in the Magellanic Clouds that the trend of mass-loss rates with period of luminosity was comparable to that of Galactic sources.…”

Section: Introductionmentioning

confidence: 89%

The mass-loss return from evolved stars to the Large Magellanic Cloud

Srinivasan

Sargent

Matsuura

et al. 2010

A&A

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We present a radiative transfer model for the circumstellar dust shell around a Large Magellanic Cloud (LMC) long-period variable (LPV) previously studied as part of the Optical Gravitational Lensing Experiment (OGLE) survey of the LMC. OGLE LMC LPV 28579 (SAGE J051306.40-690946.3) is a carbon-rich asymptotic giant branch (AGB) star for which we have Spitzer broadband photometry and spectra from the SAGE and SAGE-Spec programs along with broadband UBVIJHK s photometry. By modeling this source, we obtain a baseline set of dust properties to be used in the construction of a grid of models for carbon stars. We reproduce the spectral energy distribution of the source using a mixture of amorphous carbon and silicon carbide with 15% SiC by mass. The grain sizes are distributed according to the KMH model, with γ = 3.5, a min = 0.01 μm and a 0 = 1.0 μm. The best-fit model produces an optical depth of 0.28 for the dust shell at the peak of the SiC feature (11.3 μm), with an inner radius of about 1430 R or 4.4 times the stellar radius. The temperature at this inner radius is 1310 K. Assuming an expansion velocity of 10 km s −1 , we obtain a dust mass-loss rate of 2.5 × 10 −9 M yr −1 . We calculate a 15% variation in this mass-loss rate by testing the sensitivity of the fit to variation in the input parameters. We also present a simple model for the molecular gas in the extended atmosphere that could give rise to the 13.7 μm feature seen in the spectrum. We find that a combination of CO and C 2 H 2 gas at an excitation temperature of about 1000 K and column densities of 3 × 10 21 cm −2 and 10 19 cm −2 respectively are able to reproduce the observations. Given that the excitation temperature is close to the temperature of the dust at the inner radius, most of the molecular contribution probably arises from this region. The luminosity corresponding to the first epoch of SAGE observations is 6580 L . For an effective temperature of about 3000 K, this implies a stellar mass of 1.5−2 M and an age of 1−2.5 Gyr for OGLE LMC LPV 28579. We calculate a gas mass-loss rate of 5.0 × 10 −7 M yr −1 assuming a gas:dust ratio of 200. This number is comparable to the gas mass-loss rates estimated from the period, color and 8 μm flux of the source.

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Section: Introductionmentioning

confidence: 89%

The mass-loss return from evolved stars to the Large Magellanic Cloud

Srinivasan

Sargent

Matsuura

et al. 2010

A&A

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“…This is very different for AGB stars (see the spectrum of an AGB star SMP SMC 18 in Fig. 10, bottom), which show featureless continuum-dominated spectra (Yang et al 2004;Sloan et al 2006). Post-AGB stars (also called photo-planetary nebulae, proto-PNe) show some nebular emission lines and/or PAH features (see the spectrum of post-AGB star IRAS 01005+7910 in Fig.…”

Section: Host Galaxy Contributionmentioning

confidence: 96%

Nuclear obscuration in LINERs

González‐Martín

Masegosa

Márquez

et al. 2015

A&A

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Context. Most of the optically classified low-ionisation, narrow emission-line regions (LINERs) nuclei host an active galactic nucleus (AGN). However, how they fit into the unified model (UM) of AGN is still an open question.Aims. The aims of this work are to study at mid-infrared (mid-IR) (1) the Compton-thick nature of LINERs (i.e. hydrogen column densities of N H > 1.5 × 10 24 cm −2 ) and (2) the disappearance of the dusty torus in LINERs predicted from theoretical arguments. Methods. We have compiled all the available low spectral-resolution, mid-IR spectra of LINERs from the InfraRed Spectrograph (IRS) onboard Spitzer. The sample contains 40 LINERs. We have complemented the LINER sample with Spitzer/IRS spectra of PG QSOs, Type-1 Seyferts (S1s), Type-2 Seyferts (S2s), and StarBurst (SB) nuclei. We studied the AGN compared to the starburst content in our sample using different indicators: the equivalent width of the polycyclic aromatic hydrocarbon at 6.2 µm, the strength of the silicate feature at 9.7 µm, and the steepness of the mid-IR spectra. We classified the spectra as SB-dominated and AGN-dominated, according to these diagnostics and compared the average mid-IR spectra of the various classes. Moreover, we studied the correlation between the 12 µm luminosity, νL ν (12 µm), and the 2−10 keV energy band X-ray luminosity, L X (2−10 keV). Results. In 25 out of the 40 LINERs (i.e. 62.5%), the mid-IR spectra are not SB-dominated, similar to the comparison S2 sample (67.7%). The average spectra of both SB-dominated LINERs and S2s are very similar to the average spectrum of the SB class. The average spectrum of AGN-dominated LINERs is different from the average spectra of the other optical classes, showing a rather flat spectrum at 6−28 µm. We find that the average spectrum of AGN-dominated LINERs with X-ray luminosities L X (2−10 keV) > 10 41 erg/s is similar to the average mid-IR spectrum of AGN-dominated S2s. However, faint LINERs (i.e. L X (2−10 keV) < 10 41 erg/s) show flat spectra different from any of the other optical classes. The correlation between νL ν (12 µm) and L X (2−10 keV) for AGN nicely extends towards low luminosities only if SB-dominated LINERs are excluded and if the 2−10 keV band X-ray luminosity is corrected in Compton-thick LINER candidates. Conclusions. We find that LINERs proposed as Compton-thick candidates at X-ray wavelengths may be confirmed according to the X-ray to mid-IR luminosity relation. We show evidence that the dusty-torus disappear when their bolometric luminosity is below L bol 10 42 erg/s. We suggest that the dominant emission at mid-IR of faint LINERs might be a combination of an elliptical galaxy host (characterised by the lack of gas), a starburst, a jet, and/or ADAF emission. Alternatively, the mid-IR emission of some of these faint LINERs could be a combination of elliptical galaxy plus carbon-rich planetary nebulae. To reconcile the Compton-thick nature of a large number of LINERs without dusty-torus signatures, we suggest that the material producing the ...

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“…Fortunately, other programs produced a surplus of carbon stars, which has resulted in a series of papers on carbon stars in the SMC (Sloan et al 2006b;Lagadec et al 2007) and the LMC Leisenring et al 2008). Three of the peak-up failures resulted in serendipitous observations.…”

Section: Sample Selectionmentioning

confidence: 99%

“…We used CASPIR ( McGregor et al 1994) on the 2.3 m telescope at SSO to obtain images at J (effective wavelength 1.24 m), H (1.68 m), K (2.22 m), and narrowband L (3.59 m). Sloan et al (2006b) describe the calibration methods. Table 3 presents the photometry.…”

Section: Near-infrared Photometrymentioning

confidence: 99%

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The Magellanic Zoo: Mid‐InfraredSpitzerSpectroscopy of Evolved Stars and Circumstellar Dust in the Magellanic Clouds

Sloan

Kraemer

Wood

et al. 2008

Astrophysical Journal

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102

170

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We observed a sample of evolved stars in the Large and Small Magellanic Clouds (LMC and SMC) with the Infrared Spectrograph on the Spitzer Space Telescope. Comparing samples from the SMC, LMC, and the Galaxy reveals that the dust production rate depends on metallicity for oxygen-rich stars, but carbon stars with similar pulsation properties produce similar quantities of dust, regardless of their initial metallicity. Other properties of the oxygen-rich stars also depend on metallicity. As the metallicity decreases, the fraction of naked (i.e., dust-free) stars increases, and among the naked stars, the strength of the 8 m absorption band from SiO decreases. Our sample includes several massive stars in the LMC with long pulsation periods that produce significant amounts of dust, probably because they are young and relatively metal-rich. Little alumina dust is seen in circumstellar shells in the SMC and LMC, unlike in Galactic samples. Three oxygen-rich sources also show emission from magnesium-rich crystalline silicates. Many also show an emission feature at 14 m. The one S star in our sample shows a newly detected emission feature centered at 13.5 m. At lower metallicity, carbon stars with similar amounts of amorphous carbon in their shells have stronger absorption from molecular acetylene (C 2 H 2 ) and weaker emission from SiC and MgS dust, as discovered in previous studies.

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Mid‐Infrared Spectroscopy of Carbon Stars in the Small Magellanic Cloud

Cited by 78 publications

References 53 publications

The mass-loss return from evolved stars to the Large Magellanic Cloud

The mass-loss return from evolved stars to the Large Magellanic Cloud

Nuclear obscuration in LINERs

The Magellanic Zoo: Mid‐InfraredSpitzerSpectroscopy of Evolved Stars and Circumstellar Dust in the Magellanic Clouds

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