The Nature of Interstellar Gas toward the Pleiades Revealed in Absorption Lines

Ritchey, Adam M.; Martínez, Manuel Martínez; Pan, Kaike; Federman, S. R.; Lambert, David L.

doi:10.1086/506585

Cited by 20 publications

(28 citation statements)

References 53 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This mismatch between model and observations, might be an additional manifestation of the out-of-equilibrium chemistry, as already proposed by e.g. Zsargó & Federman (2003) and Ritchey et al (2006). The "excess" of CH abundance may be the product of CH + recombination with H 2 .…”

Section: Moleculesmentioning

confidence: 72%

Modeling of diffuse molecular gas applied to HD 102065 observations

Nehmé¹,

Bourlot²,

Boulanger

et al. 2008

A&A

View full text Add to dashboard Cite

Aims. We model a diffuse molecular cloud present along the line of sight to the star HD 102065. We compare our modeling with observations to test our understanding of physical conditions and chemistry in diffuse molecular clouds. Methods. We analyze an extensive set of spectroscopic observations which characterize the diffuse molecular cloud observed toward HD 102065. Absorption observations provide the extinction curve, H 2 , C i, CO, CH, and CH + column densities and excitation. These data are complemented by observations of C + , CO and dust emission. Physical conditions are determined using the Meudon PDR model of UV illuminated gas. Results. We find that all observational results, except column densities of CH, CH + and H 2 in its excited (J ≥ 2) levels, are consistent with a cloud model implying a Galactic radiation field (G ∼ 0.4 in Draine's unit), a density of 80 cm −3 and a temperature (60−80 K) set by the equilibrium between heating and cooling processes. To account for excited (J ≥ 2) H 2 levels column densities, an additional component of warm (∼250 K) and dense (n H ≥ 10 4 cm −3 ) gas within 0.03 pc of the star would be required. This solution reproduces the observations only if the ortho-to-para H 2 ratio at formation is ∼1. In view of the extreme physical conditions and the unsupported requirement on the ortho-to-para ratio, we conclude that H 2 excitation is most likely to be accounted for by the presence of warm molecular gas within the diffuse cloud heated by the local dissipation of turbulent kinetic energy. This warm H 2 is required to account for the CH + column density. It could also contribute to the CH abundance and explain the inhomogeneity of the CO abundance indicated by the comparison of absorption and emission spectra.

show abstract

Section: Moleculesmentioning

confidence: 72%

Modeling of diffuse molecular gas applied to HD 102065 observations

Nehmé¹,

Bourlot²,

Boulanger

et al. 2008

A&A

View full text Add to dashboard Cite

show abstract

“…For diffuse clouds the ISRF can also be estimated from steady-state gas phase chemistry (see e.g. Welty et al 2006;Ritchey et al 2006): …”

Section: The Interstellar Radiation Field Strengthmentioning

confidence: 99%

Diffuse interstellar bands in Upper Scorpius: probing variations in the DIB spectrum due to changing environmental conditions

Vos

Cox

Kaper

et al. 2011

A&A

101

177

View full text Add to dashboard Cite

Aims. We study the effects of local environmental conditions affecting the diffuse interstellar band (DIB) carriers within the Upper Scorpius subgroup of the Sco OB2 association. The aim is to reveal how the still unidentified DIB carriers respond to different physical conditions prevailing in interstellar clouds, in order to shed light on the origin of the DIB carriers. Methods. We obtained optical spectra with FEROS on the ESO 1.52 m telescope at La Silla, Chile, and measured the equivalent widths of five DIBs (at 5780, 5797, 6196, 6379, and 6613 Å) as well as those of absorption lines of di-atomic molecules (CH, CH + , CN) and atoms (K i, Ca i) towards 89 targets in the direction of Upper Scorpius. We construct a simple radiative transfer and chemical network model of the diffuse interstellar medium (ISM) sheet in front of Upp Sco to infer the effective radiation field. Results. By measuring the DIB and molecular spectrum of diffuse clouds towards 89 sightlines in the Upper Scorpius region, we have obtained a valuable statistical dataset that provides information on the physical conditions that influence the band strengths of the DIBs. Both the interstellar radiation field strength, I UV , and the molecular hydrogen fraction, f H 2 , have been derived for 55 sightlines probing the Upp Sco ISM. We discuss the relations between DIB strengths, CH and CH + line strengths, E (B−V) , I UV , and f H 2 . The ratio between the 5780 and 5797 Å DIBs reveals a (spatial) dependence on the local environment in terms of cloud density and exposure to the interstellar radiation field, reflecting the molecular nature of these DIB carriers.

show abstract

“…White (1984) studied a larger area in the Pleiades enclosing the main exciting stars and estimated densities n ∼ 400 cm −3 , whereas Gordon & Arny (1984) found n ∼ 100 cm −3 in a similar area. Ritchey et al (2006) obtained even lower values of n ∼ 46, 16, and 40 cm −3 in the lines of sight of 25 Tau, 27 Tau, and 28 Tau, respectively. Different studies, based on CO maps (Federman & Willson 1984) and on high-resolution spectra toward Pleiades stars (White 2003), have shown the gas and dust that make up the Pleiades nebula to have a significant radial velocity offset relative to the star cluster.…”

Section: Pleiades Environment and Physical Conditionsmentioning

confidence: 83%

“…by Ritchey et al (2006), and also provides a better fit to the 60.8 GHz point. Once we have obtained the spinning dust spectra for the molecular and atomic phases from spdust.2, their amplitudes, which are defined by the hydrogen column densities N H , are fitted to the measured fluxes.…”

Section: Notesmentioning

confidence: 87%

“…However, given the relatively high Galactic latitude of the Pleiades, one would expect those differences to be smaller. Therefore, instead of performing a pixel-by-pixel correction, we conservatively assume an average value of E B−V = 0.1, which is slightly larger than the mean over the 20 stars of Ritchey et al (2006). We finally obtain I corr Hα = 0.12 R, and assuming an electron temperature of 8000 K, we obtain an emission measure (EM) of EM = 0.267 cm −6 pc.…”

Section: Expected Free-free Emission From Hαmentioning

confidence: 99%

See 1 more Smart Citation

DETECTION OF ANOMALOUS MICROWAVE EMISSION IN THE PLEIADES REFLECTION NEBULA WITHWILKINSON MICROWAVE ANISOTROPY PROBEAND THE COSMOSOMAS EXPERIMENT

Génova-Santos

Rebolo

Rubiño-Martín

et al. 2011

ApJ

View full text Add to dashboard Cite

We present evidence for anomalous microwave emission (AME) in the Pleiades reflection nebula, using data from the seven-year release of the Wilkinson Microwave Anisotropy Probe and from the COSMOSOMAS (Cosmological Structures on Medium Angular Scales) experiment. The flux integrated in a 1• radius around R.A. = 56.• 24, decl. = 23.• 78 (J2000) is 2.15 ± 0.12 Jy at 22.8 GHz, where AME is dominant. COSMOSOMAS data show no significant emission, but allow one to set upper limits of 0.94 and 1.58 Jy (99.7% confidence level), respectively, at 10.9 and 14.7 GHz, which are crucial to pin down the AME spectrum at these frequencies, and to discard any other emission mechanisms which could have an important contribution to the signal detected at 22.8 GHz. We estimate the expected level of free-free emission from an extinction-corrected Hα template, while the thermal dust emission is characterized from infrared DIRBE data and extrapolated to microwave frequencies. When we deduct the contribution from these two components at 22.8 GHz, the residual flux, associated with AME, is 2.12 ± 0.12 Jy (17.7σ ). The spectral energy distribution from 10 to 60 GHz can be accurately fitted with a model of electric dipole emission from small spinning dust grains distributed in two separated phases of molecular and atomic gas, respectively. The dust emissivity, calculated by correlating the 22.8 GHz data with 100 μm data, is found to be 4.36 ± 0.17 μK (MJy sr −1 ) −1 , a value considerably lower than in typical AME clouds, which present emissivities of ∼20 μK (MJy sr −1 ) −1 , although higher than the 0.2 μK (MJy sr −1 ) −1 of the translucent cloud LDN 1780, where AME has recently been claimed. The physical properties of the Pleiades nebula, in particular its low extinction A V ∼ 0.4, indicate that this is indeed a much less opaque object than those where AME has usually been studied. This fact, together with the broad knowledge of the stellar content of this region, provides an excellent testbed for AME characterization in physical conditions different from those generally explored up to now.

show abstract

The Nature of Interstellar Gas toward the Pleiades Revealed in Absorption Lines

Cited by 20 publications

References 53 publications

Modeling of diffuse molecular gas applied to HD 102065 observations

Modeling of diffuse molecular gas applied to HD 102065 observations

Diffuse interstellar bands in Upper Scorpius: probing variations in the DIB spectrum due to changing environmental conditions

DETECTION OF ANOMALOUS MICROWAVE EMISSION IN THE PLEIADES REFLECTION NEBULA WITHWILKINSON MICROWAVE ANISOTROPY PROBEAND THE COSMOSOMAS EXPERIMENT

Contact Info

Product

Resources

About