The rich far-infrared water vapour spectrum of W Hya (original) (raw)
Related papers
Astronomy and Astrophysics, 2009
A detailed radiative transfer code has been previously used to model circumstellar ortho-H 2 O line emission towards six Mtype asymptotic giant branch stars using Infrared Space Observatory Long Wavelength Spectrometer data. Collisional and radiative excitation, including the ν 2 = 1 state, was considered. Aims. Spectrally resolved circumstellar H 2 O(1 10 -1 01 ) lines have been obtained towards three M-type AGB stars using the Odin satellite. This provides additional strong constrains on the properties of circumstellar H 2 O, in particular on the chemistry in the stellar atmosphere, and the photodissociation in the outer envelope. Methods. Infrared Space Observatory and Odin satellite H 2 O line data are used as constraints for radiative transfer models. Special consideration is taken to the spectrally resolved Odin line profiles, and the effect of excitation to the first excited vibrational states of the stretching modes (ν 1 = 1 and ν 3 = 1) on the derived abundances is estimated. A non-local, radiative transfer code based on the accelerated lambda iteration formalism is used. A statistical analysis is performed to determine the best-fit models. Results. The H 2 O abundance estimates are in agreement with previous estimates. The inclusion of the Odin data sets stronger constraints on the size of the H 2 O envelope. The H 2 O(1 10 -1 01 ) line profiles require a significant reduction in expansion velocity compared to the terminal gas expansion velocity determined in models of CO radio line emission, indicating that the H 2 O emission lines probe a region where the wind is still being accelerated. Including the ν 3 = 1 state significantly lowers the estimated abundances for the low-mass-loss-rate objects. This shows the importance of detailed modelling, in particular the details of the infrared spectrum in the range 3 to 6 µm, to estimate accurate circumstellar H 2 O abundances. Conclusions. Spectrally resolved circumstellar H 2 O emission lines are important probes of the physics and chemistry in the inner regions of circumstellar envelopes around asymptotic giant branch stars. Predictions for H 2 O emission lines in the spectral range of the upcoming Herschel/HIFI mission indicate that these observations will be very important in this context.
Astronomy and Astrophysics, 2010
Aims. A set of new, sensitive, and spectrally resolved, sub-millimeter line observations are used to probe the warm circumstellar gas around the S-type AGB star χ Cyg. The observed lines involve high rotational quantum numbers, which, combined with previously obtained lower-frequency data, make it possible to study in detail the chemical and physical properties of, essentially, the entire circumstellar envelope of χ Cyg. Methods. The data were obtained using the HIFI instrument aboard Herschel, whose high spectral resolution provides valuable information about the line profiles. Detailed, non-LTE, radiative transfer modelling, including dust radiative transfer coupled with a dynamical model, has been performed to derive the temperature, density, and velocity structure of the circumstellar envelope. Results. We report the first detection of circumstellar H 2 O rotational emission lines in an S-star. Using the high-J CO lines to derive the parameters for the circumstellar envelope, we modelled both the ortho-and para-H 2 O lines. Our modelling results are consistent with the velocity structure expected for a dust-driven wind. The derived total H 2 O abundance (relative to H 2) is (1.1 ± 0.2) × 10 −5 , much lower than that in O-rich stars. The derived ortho-to-para ratio of 2.1 ± 0.6 is close to the high-temperature equilibrium limit, consistent with H 2 O being formed in the photosphere.
Astronomy and Astrophysics, 2010
During their asymptotic giant branch evolution, low-mass stars lose a significant fraction of their mass through an intense wind, enriching the interstellar medium with products of nucleosynthesis. We observed the nearby oxygen-rich asymptotic giant branch star IK Tau using the highresolution HIFI spectrometer onboard Herschel. We report on the first detection of H 16 2 O and the rarer isotopologues H 17 2 O and H 18 2 O in both the ortho and para states. We deduce a total water content (relative to molecular hydrogen) of 6.6 × 10 −5 , and an ortho-to-para ratio of 3:1. These results are consistent with the formation of H 2 O in thermodynamical chemical equilibrium at photospheric temperatures, and does not require pulsationally induced non-equilibrium chemistry, vaporization of icy bodies or grain surface reactions. High-excitation lines of 12 CO, 13 CO, 28 SiO, 29 SiO, 30 SiO, HCN, and SO have also been detected. From the observed line widths, the acceleration region in the inner wind zone can be characterized, and we show that the wind acceleration is slower than hitherto anticipated.
ASTRONOMY AND ASTROPHYSICS Thermal H2O emission from the Herbig-Haro flow HH 54?
2013
The first detection of thermal water emission from a Herbig-Haro object is presented. The observations were performed with the Lws (Long Wavelength Spectrograph) aboard Iso (Infrared Space Observatory). Besides H 2 O, rotational lines Key words: stars: formation-ISM: molecules-ISM: jets and outflows-ISM: individual objects: HH 54-physical processes: shock waves-physical processes: radiative transfer ? Based on observations with Iso,anEsa project with instruments funded by Esa Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of Isas and Nasa (see: Kessler et al. 1996).
Astronomy & Astrophysics, 2008
Conclusions: The high water abundance found for the majority of the sources suggests that either the `normal' chemical processes are very effective in producing H2O, or else non-local thermal equilibrium atmospheric chemistry, grain surface reactions, or a release of H_2O (e.g. from icy bodies like Kuiper belt objects) play a role. We provide predictions for ortho-H2O lines in the spectral window of Herschel/HIFI.
Spectral analysis of water vapour in cool stars
Monthly Notices of the Royal Astronomical Society, 2002
M-star spectra, at wavelengths beyond 1.35mum, are dominated by water vapour, yet terrestrial water vapour makes it notoriously difficult to obtain accurate measurement from ground-based observations. We have used the short-wavelength spectrometer on the Infrared Space Observatory at four wavelength settings to cover the 2.5-3.0mum region for a range of M stars. The observations show a good match with previous
First hyperfine resolved far-infrared OH spectrum from a star-forming region
Astronomy & Astrophysics, 2011
OH is an important molecule in the H2O chemistry and the cooling budget of star-forming regions. The goal of the Herschel key program `Water in Star-forming regions with Herschel' (WISH) is to study H2O and related species during protostellar evolution. Our aim in this letter is to assess the origin of the OH emission from star-forming regions and constrain the properties of the emitting gas. High-resolution observations of the OH 2Pi1/2 J = 3/2-1/2 triplet at 1837.8 GHz (163.1 micron) towards the high-mass star-forming region W3 IRS 5 with the Heterodyne Instrument for the Far-Infrared (HIFI) on Herschel reveal the first hyperfine velocity-resolved OH far-infrared spectrum of a star-forming region. The line profile of the OH emission shows two components: a narrow component (FWHM approx. 4-5 km/s) with partially resolved hyperfine structure resides on top of a broad (FWHM approx. 30 km/s) component. The narrow emission agrees well with results from radiative transfer calculations of a spherical envelope model for W3 IRS 5 with a constant OH abundance of approx. 8e-9. Comparison with H2O yields OH/H2O abundance ratios of around 1e-3 for T > 100 K and around unity for T < 100K, consistent with the current picture of the dense cloud chemistry with freeze-out and photodesorption. The broad component is attributed to outflow emission. An abundance ratio of OH/H2O > 0.028 in the outflow is derived from comparison with results of water line modeling. This ratio can be explained by a fast J-type shock or a slower UV-irradiated C-type shock.
Astronomy & Astrophysics, 2013
Context. Understanding the physical phenomena involved in the earlierst stages of protostellar evolution requires knowledge of the heating and cooling processes that occur in the surroundings of a young stellar object. Spatially resolved information from its constituent gas and dust provides the necessary constraints to distinguish between different theories of accretion energy dissipation into the envelope. Aims. Our aims are to quantify the far-infrared line emission from low-mass protostars and the contribution of different atomic and molecular species to the gas cooling budget, to determine the spatial extent of the emission, and to investigate the underlying excitation conditions. Analysis of the line cooling will help us characterize the evolution of the relevant physical processes as the protostar ages. Methods. Far-infrared Herschel-PACS spectra of 18 low-mass protostars of various luminosities and evolutionary stages are studied in the context of the WISH key program. For most targets, the spectra include many wavelength intervals selected to cover specific CO, H2O, OH, and atomic lines. For four targets the spectra span the entire 55-200 μm region. The PACS field-of-view covers ~47" with the resolution of 9.4". Results. Most of the protostars in our sample show strong atomic and molecular far-infrared emission. Water is detected in 17 out of 18 objects (except TMC1A), including 5 Class I sources. The high-excitation H2O 818-707 63.3 μm line (Eu/kB = 1071 K) is detected in 7 sources. CO transitions from J = 14-13 up to J = 49 - 48 are found and show two distinct temperature components on Boltzmann diagrams with rotational temperatures of ~350 K and ~700 K. H2O has typical excitation temperatures of ~150 K. Emission from both Class 0 and I sources is usually spatially extended along the outflow direction but with a pattern that depends on the species and the transition. In the extended sources, emission is stronger off source and extended on &≥10,000 AU scales; in the compact sample, more than half of the flux originates within 1000 AU of the protostar. The H2O line fluxes correlate strongly with those of the high-J CO lines, both for the full array and for the central position, as well as with the bolometric luminosity and envelope mass. They correlate less strongly with OH fluxes and not with [O I] fluxes. In contrast, [O I] and OH often peak together at the central position. Conclusions. The PACS data probe at least two physical components. The H2O and CO emission very likely arises in non-dissociative (irradiated) shocks along the outflow walls with a range of pre-shock densities. Some OH is also associated with this component, most likely resulting from H2O photodissociation. UV-heated gas contributes only a minor fraction to the CO emission observed by PACS, based on the strong correlation between the shock-dominated CO 24-23 line and the CO 14-13 line. [O I] and some of the OH emission probe dissociative shocks in the inner envelope. The total far-infrared cooling is dominated by H2O and CO, with the fraction contributed by [O I] increasing for Class I sources. Consistent with previous studies, the ratio of total far-infrared line emission over bolometric luminosity decreases with the evolutionary state.
The Astrophysical Journal, 2011
We present high signal-to-noise, moderate spectral resolution (R ∼ 2000 − 2500) near-infrared (0.8 − 5.0 µm) spectroscopy of the nearby T Tauri star TW Hya. By comparing the spectrum and the equivalent widths of several atomic and molecular features with those for stars in the IRTF near-infrared library, we revise the spectral type to M2.5V, which is later than usually adopted (K7V). This implies a substantially cooler stellar temperature than previously assumed. Comparison with various pre-main sequence models suggests that TW Hya is only ∼ 3 Myr old; much younger than the usually adopted 8 − 10 Myr. Analysis of the relative strengths of the H lines seen in the spectrum yields estimates for the temperature and density of the emitting region of T e ≥ 7500 K and n e ∼ 10 12 − 10 13 cm −3. The thickness of the emitting region is 10 2 − 10 4 km and the covering fraction is f * ∼ 0.04. Our derived physical parameter values agree with the predictions of the magnetospheric accretion scenario. The highest signal-to-noise H lines have profiles that indicate multiple emission components. We derive an excess spectrum (above that of the M2.5V template) that peaks in the H band. Although our derived veiling values, ∼ 0.1, agree with previous estimates, the excess spectrum does not match that of current models in which this flux is generated by an inner optically thin disk. We suggest that the excess flux spectrum instead reflects the differences in atmospheric opacity, gravity, and age between TW Hya and older, higher gravity field M2.5 dwarfs.
Signatures of hot hydrogen in the atmosphere of the extrasolar planet HD209458b
Nature, 2007
About ten per cent of the known extrasolar planets are gas giants that orbit very close to their parent stars. The atmospheres of these 'hot Jupiters' are heated by the immense stellar irradiation 1-5 . In the case of the planet HD 209458b, this energy deposition results in a hydrodynamic state in the upper atmosphere, allowing for sizeable expansion and escape of neutral hydrogen gas 2-6 . HD 209458b was the first extrasolar planet discovered that transits in front of its parent star 7 . The size of the planet can be measured using the total optical obscuration of the stellar disk during an observed transit, and the structure and composition of the planetary atmosphere can be studied using additional planetary absorption signatures in the stellar spectrum. Here we report the detection of absorption by hot hydrogen in the atmosphere of HD 209458b. Previously, the lower atmosphere and the full extended upper atmosphere of HD 209458b have been observed 2,6,8 , whereas here we probe a layer where the escaping gas forms in the upper atmosphere of HD 209458b.