A low density molecular cloud in the vicinity of the Pleiades

Federman, S. R.; Willson, R. F.

doi:10.1086/162347

Cited by 9 publications

(17 citation statements)

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“…The model is appropriate for a diffuse cloud with large molecular content but does not include dark-cloud chemistry. As argued by Federman & Willson (1984), the CO column density from the densest, most opaque portion of the cloud, N(CO) ∼ 4.5 × 10 17 cm −2 , while larger than the values measured in diffuse gas, is significantly lower than those measured toward the centers of dark clouds. The Pleiades cloud is not, therefore, an intermediate zone between diffuse and dark clouds but simply a much less opaque molecular cloud than is normally observed in the Taurus region.…”

Section: Ultraviolet-pumping Model Of H 2 Rotational Excitationmentioning

confidence: 79%

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

Ritchey

Martínez

Pan

et al. 2006

ApJ

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We present high-resolution, high signal to noise absorption-line observations of CN, Ca II, Ca I, CH + , and CH along twenty lines of sight toward members of the Pleiades. The acquired data enable the most detailed study to date of the interaction between cluster stars and the surrounding interstellar gas. Total equivalent widths are consistent with previous investigations except where weaker features are detected owing to our greater sensitivity. Mean b-values for the molecular species indicate that toward most of the Pleiades CH is associated with the production of CH + rather than CN. An analysis of radial velocities reveals a kinematic distinction between ionized atomic gas and molecular and neutral gas. Molecular components are found with velocities in the local standard of rest of either ∼ +7 km s −1 or ∼ +9.5 km s −1 , with the higher-velocity components associated with the strongest absorption. Atomic gas traced by Ca II shows a strong central component at v LSR ∼ +7 km s −1 exhibiting velocity gradients indicative of cloud-cluster interactions. Gas density estimates derived from measured CH/CH + column density ratios show good agreement with those inferred from H 2 rotational populations, yielding typical values of n ∼ 50 cm −3 . Our models do not include the important time-dependent effects on CH + formation which may ultimately be needed to extract physical conditions in these clouds.

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Section: Ultraviolet-pumping Model Of H 2 Rotational Excitationmentioning

confidence: 79%

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

Ritchey

Martínez

Pan

et al. 2006

ApJ

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“…High-resolution spectra of the brightest Pleiades stars as well as CO maps toward the cluster show that there is gas as well as dust present and that the (primary) interstellar cloud has a significant radial velocity offset relative to the Pleiades (White 2003;Federman & Willson 1984). The gas and dust, therefore, are not a remnant from the formation of the cluster but are simply evidence of a transitory event as this small cloud passes by the cluster in our line of sight (see also Breger 1986).…”

Section: Mid-ir Observations Of Dust and Polycyclic Aromatic Hydrocarmentioning

confidence: 99%

Near‐ and Mid‐Infrared Photometry of the Pleiades and a New List of Substellar Candidate Members

Stauffer

Hartmann

Fazio

et al. 2007

ASTROPHYS J SUPPL S

118

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We make use of new near-and mid-IR photometry of the Pleiades cluster in order to help identify proposed cluster members. We also use the new photometry with previously published photometry to define the single-star mainsequence locus at the age of the Pleiades in a variety of color-magnitude planes. The new near-and mid-IR photometry extend effectively 2 mag deeper than the 2MASS All-Sky Point Source catalog, and hence allow us to select a new set of candidate very low-mass and substellar mass members of the Pleiades in the central square degree of the cluster. We identify 42 new candidate members fainter than K s ¼ 14 (corresponding to 0.1 M ). These candidate members should eventually allow a better estimate of the cluster mass function to be made down to of order 0.04 M . We also use new IRAC data, in particular the images obtained at 8 m, in order to comment briefly on interstellar dust in and near the Pleiades. We confirm, as expected, that-with one exception-a sample of low-mass stars recently identified as having 24 m excesses due to debris disks do not have significant excesses at IRAC wavelengths. However, evidence is also presented that several of the Pleiades high-mass stars are found to be impacting with local condensations of the molecular cloud that is passing through the Pleiades at the current epoch.

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“…The strong emission ∼15 south of 23 Tau is originated in the Merope molecular cloud, identified by Federman & Willson (1984) in CO maps. Another two bright knots of infrared emission are seen in the IRAS maps concentrated around the stars 17 Tau and 20 Tau.…”

Section: Pleiades Environment and Physical Conditionsmentioning

confidence: 94%

“…The physical properties of the gas in different positions of the whole complex have been studied by different authors. Federman & Willson (1984) obtained gas densities n ∼ 300-500 cm −3 and temperatures T g ∼ 20 K from molecular line observations in the Merope molecular cloud. They found column densities intermediate between diffuse and dark clouds, and concluded that Merope is indeed much less opaque than typical Taurus clouds.…”

Section: Pleiades Environment and Physical Conditionsmentioning

confidence: 99%

“…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. A corollary of this is that the Pleiades stars were not formed out of this surrounding material but, more likely, the spatial association between the stars and the interstellar gas is the result of a chance encounter between the cluster and one or more approaching clouds.…”

Section: Pleiades Environment and Physical Conditionsmentioning

confidence: 99%

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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

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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.

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A low density molecular cloud in the vicinity of the Pleiades

Cited by 9 publications

References 0 publications

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

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

Near‐ and Mid‐Infrared Photometry of the Pleiades and a New List of Substellar Candidate Members

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

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