Re-examining Larson's Scaling Relationships in Galactic Molecular Clouds

The properties of Galactic molecular clouds tabulated by Solomon etal (1987) (SRBY) are re-examined using the Boston University-FCRAO Galactic Ring Survey of 13CO J=1-0 emission. These new data provide a lower opacity tracer of molecular clouds and improved angular and spectral resolution than previous surveys of molecular line emission along the Galactic Plane. We calculate GMC masses within the SRBY cloud boundaries assuming LTE conditions throughout the cloud and a constant H2 to 13CO abundance, while accounting for the variation of the 12C/13C with Galacto-centric radius. The LTE derived masses are typically five times smaller than the SRBY virial masses. The corresponding median mass surface density of molecular hydrogen for this sample is 42 Msun/pc^2, which is significantly lower than the value derived by SRBY (median 206 Msun/pc^2) that has been widely adopted by most models of cloud evolution and star formation. This discrepancy arises from both the extrapolation by SRBY of velocity dispersion, size, and CO luminosity to the 1K antenna temperature isophote that likely overestimates the GMC masses and our assumption of constant 13CO abundance over the projected area of each cloud. Owing to the uncertainty of molecular abundances in the envelopes of clouds, the mass surface density of giant molecular clouds could be larger than the values derived from our 13CO measurements. From velocity dispersions derived from the 13CO data, we find that the coefficient of the cloud structure functions, vo=sigma_v/R^{1/2}, is not constant, as required to satisfy Larson's scaling relationships, but rather systematically varies with the surface density of the cloud as Sigma^{0.5} as expected for clouds in self-gravitational equlibrium.Comment: Accepted by ApJ. Newest version includes modifications from the refere

Shakespearean allusion and the detective fiction of Georgette Heyer

This essay argues that Shakespearean allusion is a recurrent and important factor in the detective novels of Georgette Heyer. Though the master text for Heyer is Hamlet, a variety of Shakespeare plays are referred to, and mention of them functions in multiple ways. Quotations from Shakespeare reveal truths about the characters and comment on their situations and personalities. They also afford points of entry for people previously unacquainted to talk to each other, and finally they have effects in terms of genre, since their presence can, with equal facility, tend towards comic relief (in line with a tradition in Golden Age crime fiction of using Macbeth in particular to comic effect) or work to add gravitas and resonance. The use of Shakespearean allusion is thus central to Heyer’s technique. This article is published as part of a collection to commemorate the 400th anniversary of William Shakespeare’s death

\u3cem\u3eLeptodactylus mystacinus\u3c/em\u3e

Adult Leptodactylus mystacinus are of moderate size, the head is as wide as long, and the hind limbs are moderately short (see Table; Heyer and Thompson 2000 provided definitions of adult size and leg length categories for Leptodactylus). Male vocal sacs are not visible externally or at best are weakly expanded laterally and slightly darker than female throats. Male snouts are more spatulate than those of females. Male forearms are not hypertrophied. Males lack asperities on the thumbs and chest. One or two pairs of dorsolateral folds (indicated by dark/light outlining in indifferently preserved specimens) are present: one distinct more dorsal pair extends from behind the eye (often with a gap with the fold beginning at a level above the tympanum) to the upper groin; a second pair, either complete or interrupted, extends from above the forearm insertion at the same level as the dorsal portion of the supratympanic fold and extends to the groin along the flanks. The toe tips are narrow. The toes lack fringes or fleshy ridges. The upper shank has many or scattered distinct white tubercles. The outer tarsus almost always (94%) has many or scattered distinct white tubercles. The sole of the foot usually (75%) has distinct scattered to many white tubercles, sometimes (25%) the white tubercles are absent

Leptodactylus cunicularius Sazima and Bokermann Rabbit-burrow Frog

Adult Leptodactylus cunicularius are moderately small. The head is longer than wide and the hind limbs are long (Table 1; Heyer and Thompson 2000 provided definitions of adult size and leg length categories for Leptodactylus). Male vocal sacs are internal, not externally expanded. The snout is protruding, not sexually dimorphic. Male forearms are not hypertrophied and males lack asperities on the thumbs and chest. The dorsum is variegated with small, often confluent, spots and blotches. There is a very thin interrupted mid-dorsal light stripe (pinstripe). Usually, there is a noticeable light, irregular, elongate, mid-dorsal blotch in the scapular region. The supratympanic fold is not marked differently from the surrounding region. A weak to distinct pair of interrupted (partial or along entire length) dorsolateral folds extends from the posterior portion of the eye, passing just lateral to the sacral bones and ending in the upper groin region of the leg; the folds are usually subtly highlighted with marginally lighter stripes than the surrounding dorsal region

Turbulent Driving Scales in Molecular Clouds

Supersonic turbulence in molecular clouds is a dominant agent that strongly affects the clouds' evolution and star formation activity. Turbulence may be initiated and maintained by a number of processes, acting at a wide range of physical scales. By examining the dynamical state of molecular clouds, it is possible to assess the primary candidates for how the turbulent energy is injected. The aim of this paper is to constrain the scales at which turbulence is driven in the molecular interstellar medium, by comparing simulated molecular spectral line observations of numerical magnetohydrodynamic (MHD) models and molecular spectral line observations of real molecular clouds. We use principal component analysis, applied to both models and observational data, to extract a quantitative measure of the driving scale of turbulence. We find that only models driven at large scales (comparable to, or exceeding, the size of the cloud) are consistent with observations. This result applies also to clouds with little or no internal star formation activity. Astrophysical processes acting on large scales, including supernova-driven turbulence, magnetorotational instability, or spiral shock forcing, are viable candidates for the generation and maintenance of molecular cloud turbulence. Small scale driving by sources internal to molecular clouds, such as outflows, can be important on small scales, but cannot replicate the observed large-scale velocity fluctuations in the molecular interstellar medium.Comment: 8 pages, 7 figures, accepted for publication in A&

CO Abundance Variations in the Orion Molecular Cloud

Infrared stellar photometry from 2MASS and spectral line imaging observations of 12CO and 13CO J = 1-0 line emission from the FCRAO 14m telescope are analysed to assess the variation of the CO abundance with physical conditions throughout the Orion A and Orion B molecular clouds. Three distinct Av regimes are identified in which the ratio between the 13CO column density and visual extinction changes corresponding to the photon dominated envelope, the strongly self-shielded interior, and the cold, dense volumes of the clouds. Within the strongly self-shielded interior of the Orion A cloud, the 13CO abundance varies by 100% with a peak value located near regions of enhanced star formation activity. The effect of CO depletion onto the ice mantles of dust grains is limited to regions with AV > 10 mag and gas temperatures less than 20 K as predicted by chemical models that consider thermal-evaporation to desorb molecules from grain surfaces. Values of the molecular mass of each cloud are independently derived from the distributions of Av and 13CO column densities with a constant 13CO-to-H2 abundance over various extinction ranges. Within the strongly self-shielded interior of the cloud (Av > 3 mag), 13CO provides a reliable tracer of H2 mass with the exception of the cold, dense volumes where depletion is important. However, owing to its reduced abundance, 13CO does not trace the H2 mass that resides in the extended cloud envelope, which comprises 40-50% of the molecular mass of each cloud. The implied CO luminosity to mass ratios, M/L_{CO}, are 3.2 and 2.9 for Orion A and Orion B respectively, which are comparable to the value (2.9), derived from gamma-ray observations of the Orion region. Our results emphasize the need to consider local conditions when applying CO observations to derive H2 column densities.Comment: Accepted for publication in MNRAS. 21 pages, 14 figure

The Molecular Gas Distribution and Schmidt Law in M33

The relationship between the star formation rate and surface density of neutral gas within the disk of M33 is examined with new imaging observations of CO J=1-0 emission gathered with the FCRAO 14m telescope and IRAS HiRes images of the 60 micron and 100 micron emission. The Schmidt law, Sigma_SFR ~ Sigma_gas^n, is constructed using radial profiles of the HI 21cm, CO, and far infrared emission. A strong correlation is identified between the star formation rate and molecular gas surface density. This suggests that the condensation of giant molecular clouds is the limiting step to star formation within the M33 disk. The corresponding molecular Schmidt index, n_{mol}, is 1.36 +/- 0.08. The star formation rate has a steep dependence on total mass gas surface density, (Sigma_{HI}+Sigma_{H_2}), owing to the shallow radial profile of the atomic gas which dominates the total gas surface density for most radii. The disk pressure of the gas is shown to play a prominent role in regulating the molecular gas fraction in M33.Comment: 19 pages + 5 figures. Accepted for publication in Ap

\u3cem\u3eLeptodactylus cunicularius\u3c/em\u3e

Adult Leptodactylus cunicularius are moderately small. The head is longer than wide and the hind limbs are long (Table 1; Heyer and Thompson 2000 provided definitions of adult size and leg length categories for Leptodactylus). Male vocal sacs are internal, not externally expanded. The snout is protruding, not sexually dimorphic. Male forearms are not hypertrophied and males lack asperities on the thumbs and chest. The dorsum is variegated with small, often confluent, spots and blotches. There is a very thin interrupted mid-dorsal light stripe (pinstripe). Usually, there is a noticeable light, irregular, elongate, mid-dorsal blotch in the scapular region. The supratympanic fold is not marked differently from the surrounding region. A weak to distinct pair of interrupted (partial or along entire length) dorsolateral folds extends from the posterior portion of the eye, passing just lateral to the sacral bones and ending in the upper groin region of the leg; the folds are usually subtly highlighted with marginally lighter stripes than the surrounding dorsal region. Another pair of interrupted, irregular dorsal folds may or may not be visible on either side of the dorsum mid-line. A pair of interrupted (along entire length) lateral folds extends from the posterior dorsal portion of the tympanic fold to the mid-groin level at the leg juncture; the folds are usually slightly lighter in color than the adjacent flanks. The toe tips are rounded, not dilated. The toes lack lateral ridges or fringes and either lack or have a trace of basal webbing between toes II-III-IV. The dorsal surface of the shank lacks tubercles and has weakly developed longitudinal folds, not differentially patterned. The posterior surface of the tarsus lacks tubercles. The sole of the foot is smooth but with small irregular light spots of the same size as light tubercles found in other species. The upper lip usually has a distinct light cream or tan stripe from just behind the snout tip, passing under the eye and tympanum and continuing through the commissural gland; if lacking, the upper lip region is homogeneously colored. The belly is cream-colored, with or without a few small tan blotches on the lateral-most extent of the belly. The posterior surface of the thigh ranges from an indistinct to a labyrinthine pattern of darker and lighter browns; usually there are a series of light dots on the lower posterior thigh where light stripes occur in other species

\u3cem\u3eLeptodactylus fragilis\u3c/em\u3e (Brocchi): White-lipped Thin-toed Frog

Adult Leptodactylus fragilis are small. The head is longer than wide, and the hind limbs are moderately long (Table 1; Heyer and Thompson 2000 provided definitions of adult size and leg length categories for Leptodactylus). Male vocal sacs are laterally expanded and range from lightly gray speckled to darkly pigmented. Male snout is spatulate; female snout is rounded. Male forearms are not hypertrophied and males lack asperities on the thumbs and chest. The dorsum is spotted or blotched with dark markings, which are often chevron-shaped and sometimes confluent. The supratympanic fold is dark brown. A pair of dorsolateral folds is usually poorly developed, extending from the posterior portion of the eye, passing just lateral to the sacral bones and ending in the upper groin region at the leg; the folds are often highlighted by dark and/or light stripes. A pair of lateral folds extends from the posterior dorsal portion of the tympanic fold to the midgroin level at the leg juncture; the folds are often interrupted and/or poorly developed and are usually of lighter color than the adjacent flanks. The toe tips are rounded, either of equal diameter or slightly greater than the toe portion immediately behind the tip. The toes either lack lateral ridges and basal webbing or have very weakly developed lateral ridges (most developed proximally) and a trace of basal webbing between some or all toes 1-11-111-IV. The dorsal surface of the shank is usually covered with many white tubercles, or sometimes the white tubercles are few and scattered. The posterior surface of the tarsus either has many white tubercles (89%), or is smooth (11%). The sole of the foot always has many white tubercles. A light lip stripe extending from under the nostrils, passing under the eye and tympanum and continuing through the commissural gland is usually poorly developed (97%) or rarely distinct (3%). An interrupted mid-dorsal dark pin-stripe is occasionally present. The belly is often cream colored (lacking melanophores), it may have a scattering of melanophores to scattered diffuse dark blotches anteriorly and on the sides, or there may be scattered melanophores over the entire belly. The posterior surface of the thigh usually has a very distinct light longitudinal stripe on the lower half (66%), often moderately distinct (33%), or rarely absent (1 %)