Near-IR spectroscopy of OH/IR stars in the Galactic centre

Vanhollebeke, E.; Blommaert, J. A. D. L.; Schultheis, M.; Aringer, B.; Lançon, A.

doi:10.1051/0004-6361:20065194

Cited by 9 publications

(9 citation statements)

References 24 publications

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“…Schultheis et al (2003) note the typical errors on metallicities determined by this method to be about 0.1 dex. Using equivalent widths of the same near-infrared lines reported by Vanhollebeke et al (2006), OH359 is found to have [Fe/H] = -0.81. The distribution of metallicities of the Galactic Bulge star sample of Schultheis et al (2003) spans [Fe/H] from 0.5 down to < -2.0 dex, with the histogram of metallicities peaking around -0.3 dex.…”

Section: Gas/dust Ratiosmentioning

confidence: 68%

“…The Galactic Bulge is an ideal place to make such determinations, as the distance to the stars is well-known (∼ 8 kpc), which reduces uncertainty in these stars' other properties (e.g., luminosity). By determining reliable gas-to-dust ratios for these stars, for which we also know metallicity (see Schultheis et al 2003;Vanhollebeke et al 2006), we hope to be able to determine gas-to-dust ratios for lower-metallicity environments, like the Magellanic Clouds. We note specifically that OH359, E51, and A12 have metallicities very similar to that of the Small Magellanic Cloud of [Fe/H] = -0.64 (Russell & Dopita 1992;Rolleston et al 1999), and A51 has a metallicity quite similar to that of the Large -15 -Magellanic Cloud, which has [Fe/H] = -0.30 (Russell & Dopita 1992); therefore, our work applies to studies of mass loss in the Magellanic Clouds.…”

Section: Gas/dust Ratiosmentioning

confidence: 99%

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COJ= 2-1 EMISSION FROM EVOLVED STARS IN THE GALACTIC BULGE

Sargent¹,

Patel²,

Meixner³

et al. 2013

ApJ

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We observe a sample of 8 evolved stars in the Galactic Bulge in the CO J=2-1 line using the Submillimeter Array (SMA) with angular resolution of 1-4 arcseconds. These stars have been detected previously at infrared wavelengths, and several of them have OH maser emission. We detect CO J=2-1 emission from three of the sources in the sample: OH 359.943 +0.260, [SLO2003] A12, and [SLO2003] A51. We do not detect the remaining 5 stars in the sample because of heavy contamination from the galactic foreground CO emission. Combining CO data with observations at infrared wavelengths constraining dust mass loss from these stars, we determine the gas-to-dust ratios of the Galactic Bulge stars for which CO emission is detected. For OH 359.943 +0.260, we determine a gas mass-loss rate of 7.9 (± 2.2) ×10 −5 M ⊙ yr −1 and a gas-to-dust ratio of 310 (± 89). For [SLO2003] A12, we find a gas mass-loss rate of 5.4 (± 2.8) ×10 −5 M ⊙ yr −1 and a gas-to-dust ratio of 220 (± 110). For [SLO2003] A51, we find a gas massloss rate of 3.4 (± 3.0) ×10 −5 M ⊙ yr −1 and a gas-to-dust ratio of 160 (± 140), reflecting the low quality of our tentative detection of the CO J=2-1 emission from A51. We find the CO J=2-1 detections of OH/IR stars in the Galactic Bulge require lower average CO J=2-1 backgrounds.-2 -Subject headings: circumstellar matter -infrared: stars IntroductionAt the end of a star's life, it returns material back to the interstellar medium from which it emerged. This mass loss begins in the first red giant phase of a star's life (e.g., Groenewegen 2012). Observations show gas mass loss from red giant stars (Dupree et al. 2009), but very little in the way of dust mass loss from red giants (McDonald et al. 2011). During the red giant phase, the mass loss is relatively weak, but it increases dramatically in the Asymptotic Giant Branch (AGB) phase. The dust grains that form around AGB stars experience radiation pressure from the star, pushing them outwards, and they, in turn, push on the circumstellar gas, driving the gas outwards along with the dust (e.g., Forrest 1974). Detailed axisymmetric models by Woitke (2006) confirm this picture for Carbon-rich (C-rich) AGB stars. Bladh & Höfner (2012) confirm this idea also works for Oxygen-rich (O-rich) AGB stars, which produce silicate dust, but require the dust grains to be Mg-rich, being highly transparent in the infrared, and to grow to 0.1-1 µm sizes in order to have the large scattering cross-sections necessary to experience radiation pressure sufficient to push the grains outward to drive the mass outflow. The mass-loss rate is an important parameter in characterizing the life of a star and also in constructing galaxy evolution models. For AGB stars, we have been estimating dust mass-loss rates through fitting optical through mid-infrared spectral energy distributions (SEDs; plots of flux versus wavelength) for stars in the Large Magellanic Cloud (Riebel et al. 2012) using radiative transfer models of emission from dust shells around stars (e.g., see the "GRAMS" models constructed by...

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Section: Gas/dust Ratiosmentioning

confidence: 68%

Section: Gas/dust Ratiosmentioning

confidence: 99%

COJ= 2-1 EMISSION FROM EVOLVED STARS IN THE GALACTIC BULGE

Sargent¹,

Patel²,

Meixner³

et al. 2013

ApJ

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“…Such errors were noted as a difficulty in the measurement of individual metal lines by Vanhollebeke et al (2006). In order to verify this, we added random noise to the data at the level of a few percent, i.e.…”

Section: Methodsmentioning

confidence: 99%

Near-IR spectra of red supergiants and giants

Lançon¹,

Hauschildt

Ladjal

et al. 2007

A&A

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Context. It remains difficult to interpret the near-IR emission of young stellar populations. One main reason is our incomplete understanding of the spectra of luminous red stars. Aims. This work provides a grid of theoretical spectra of red giant and supergiant stars, that extends through optical and near-IR wavelengths. For the first time, models are also provided with modified surface abundances of C, N and O, as a step towards accounting for the changes that occur due to convective dredge-up in red supergiants or may occur at earlier evolutionary stages in the case of rotation. The aims are (i) to assess how well current models reproduce observed spectra, in particular in the near-IR; (ii) to quantify the effects of the abundance changes on the spectra; and (iii) to determine how these changes affect estimates of fundamental stellar parameters. Methods. Spectra are computed with the model atmosphere code PHOENIX and compared with a homogeneous set of observations. Although the empirical spectra have a resolution of only λ/∆λ ∼ 1000, we emphasize that models must be calculated at high spectral resolution in order to reproduce the shapes of line blends and molecular bands. Results. Giant star spectra of class III can be fitted extremely well at solar metallicity down to ∼3400 K, where difficulties appear in the modelling of near-IR H 2 O and TiO absorption bands. Luminous giants of class II can be fitted well too, with modified surface abundances preferred in a minority of cases, possibly indicating mixing in excess of standard first dredge-up. Supergiant stars show a larger variety of near-IR spectra, and good fits are currently obtained for about one third of the observations only. Modified surface abundances help reproducing strong CN bands, but do not suffice to resolve the difficulties. The effect of the abundance changes on the estimated T eff depends on the wavelength range of observation and can amount several 100 K. Conclusions. While theoretical spectra for giant stars are becoming very satisfactory, red supergiants require further work. The model grid must be extended, in particular to larger micro-turbulent velocities. Some observed spectra may call for models with even lower gravities than explored here (and therefore probably stellar winds), and/or with more extreme abundances than predicted by standard non-rotating evolution models. Non-static atmospheres models should also be envisaged.

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“…Unfortunately, although the same kind of relation should be expected, nothing can be said about the behaviour of the Ca feature. The ranges used to derive this equivalent width are influenced by more metallic lines and molecular bands (for example Ni, Sc and the CN band, see Vanhollebeke et al 2006, for a detailed list and discussion) than the ones for the other two features, thus making the modelling and extrapolation between resolutions harder. As a result, over the range of metallicities computed for the NextGen library (a grid at [M/H] = 0.0, −0.3, −0.5, −0.7), the equivalent widths derived are restricted to EW(Ca) < 3, while our sample distribution peaks at EW(Ca) ∼ 5.…”

Section: Equivalent Widthsmentioning

confidence: 99%

Metallicity distribution of red giants in the Inner Galaxy from near infrared spectra

González-Fernández

Cabrera-Lavers

Hammersley

et al. 2007

A&A

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Context. The existence in the Milky Way of either a long thin bar with a half length of 4.5 kpc and a position angle of around 45• with respect to the Sun-Galactic centre line or a bulge+bar complex, thicker and shorter, with a smaller tilt respect to the Sun-GC line, has been a matter of discussion in recent decades. Aims. In this paper, we present low resolution (R = 500) near-infrared spectra for selected and serendipitous sources in six inner in-plane Galactic fields at l = 7• , 12• , 15• , 20• , 26• and 27• , with the aim of analysing the stellar content present in those fields. Methods. From the equivalent widths of the main features of the K band spectra (the NaI, CaI and CO bandheads) we have derived the metallicities of the sources by means of the empirical scale obtained by Ramírez et al. (2000, AJ, 120, 833) and Frogel et al. (2001, AJ, 122, 1896 for luminous red giants. Results. Our results show how the mean metallicity of the sample varies with Galactic longitude. We find two groups of stars, one whose [Fe/H] is similar to the values obtained for the bulge in other studies (Molla et al. 2000, MNRAS, 316, 345; Schultheis et al. 2003, A&A, 405, 531), and a second one with a metallicity similar to that of the inner parts of the disc (Rocha-Pinto et al. 2006, A&A, 453, L9). The relative density of both groups of stars in our sample varies in a continuous way from the bulge to the disc. This could hint at the existence of a single component apart from the disc and bulge, running from l = 7• to l = 27• and able to transport disc stars inwards and bulge stars outwards, which could be the Galactic bar that has been detected in previous works as an overdensity of stars located at those galactic coordinates (Hammersley et

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Near-IR spectroscopy of OH/IR stars in the Galactic centre

Cited by 9 publications

References 24 publications

COJ= 2-1 EMISSION FROM EVOLVED STARS IN THE GALACTIC BULGE

COJ= 2-1 EMISSION FROM EVOLVED STARS IN THE GALACTIC BULGE

Near-IR spectra of red supergiants and giants

Metallicity distribution of red giants in the Inner Galaxy from near infrared spectra

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