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

\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

\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 savagei\u3c/em\u3e

Adult Leptodactylus savagei are large, the head is as wide as long or usually wider than long, and the hind limbs are moderate in length (Table 1; Heyer and Thompson (2000) provided definitions of adult size and leg length categories for Leptodactylus). Male vocal sacs are not visible externally. Sexually active males have hypertrophied forearms, usually 1 large black spine on each thumb, rarely with 1 large spine and a prepollical bump, and a pair of black chest spines. A pair of entire dorsolateral folds extend anteriorly from at least one_half to full distance from eye to groin, the dorsolateral folds are rarely interrupted. Flank folds (diverging from the supratympanic fold at the uppermost posterior portion of the tympanum and extending as far as the lower flank at mid_body level) range from entire (often) to only a dark spot/wart (rarely) in the area where the fold would be between the tympanum and shoulder. Lateral folds are not distinguishable. The toe tips are rounded and either barely wider than or of equal width as the toes immediately behind the tips. The toes have weak to noticeable lateral ridges and either lack any web or (usually) have vestigial webbing between toes I-II-III or I-II-III-IV. Metamorphic and slightly larger juveniles lack webbing and either have very weak lateral ridges or lack them. The upper shank surfaces almost always have some texture, including a shagreen and/or small black or white tubercles. The outer surface of the tarsus may either be smooth or with a shagreen or small black or white tubercles. The sole of the foot is typically smooth, lacking texture

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

\u3cem\u3eLeptodactylus syphax\u3c/em\u3e

Adult Leptodactylus syphax are moderately sized (males 58-83 mm, females 70-90 mm SVL). The head is about as long as wide, but usually is just wider than long. The hind limbs are moderately short (Table 1; Heyar and Thompson 2000 provided definitions of adult size and leg length categories for Leptodactylus). Male vocal sacs are laterally expanded, tan, and not darker than the adjacent throat. The male snout is not spatulate, the snout profile is rounded to obtuse in both sexes. Male arms are hypertrophied during the breeding season in sexually active males. The male thumb has two large, sharp, black spines; a pair of black chest spine patches has sharp, protruding spines. The dorsum is indistinctly patterned with dark, poor1y defined spots or blotches, sometimes the spots/blotches are regularly distributed. A dark posteriorly-directed triangular interorbital mark is variably present. The supratympanic fold is either the same color as or noticeably darker than the tan or brown surrounding area. There are no dorso-lateral folds. The dorsum is smooth to weakly rugose with large white tubercles limited to the sacral and postsacral region. The toe tips are rounded and are either weakly or noticeably swollen with a diameter greater than the region immediately behind the toe tip. The toes usually lack any lateral fringe or ridge or basal webbing; rarely the toes have weak ridges or a trace of webbing between toes II-III-IV. The dorsal surface of the shank has scattered white or blacktipped tubercles. The posterior surface of the tarsus and sole of the foot are either smooth or have a few large white or black-tipped tubercles. The upper lip has poorly defined to distinct vertical bars, one between the nostril and eye and two underneath the eye, or a complex dark and light pattern. There is no mid-dorsal stripe. The belly is lightly to moderately mottled with light gray or brown markings. The posterior surfaces of the thighs are boldly patterned with various-sized light tan and brown markings and lack a light longitudinal stripe on the lower halves

\u3cem\u3eLeptodactylus pentadactylus\u3c/em\u3e

Adult Leptodactylus pentadactylus (Figure 1) are large, the head is about as wide as long, 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 not visible externally or are moderately expanded as a single sac. Sexually active males usually do not have hypertrophied forearms (the largest male examined, 195 mm SVL, has very weakly hypertrophied forearms), only the largest males have a single small to moderate size black spine on each thumb. No males have chest spines. Dorsolateral folds are usually entire from the eye to at least the sacrum. Flank folds (diverging from the supratympanic fold at the uppermost portion of the tympanum) are variable, either continuous or interrupted, often extending from the tympanum to the lower flank, or only to the shoulder. The toe tips are rounded, just wider than the adjacent phalanges. The toes have prominent lateral ridges. A trace of basal webbing occurs among all toes, or toes I–II–III–IV or II–III–IV. The upper shank and outer tarsal surfaces are smooth, shagreened, or have several white or black tubercles. The sole of the foot texture is usually smooth, a few individuals have no more than a few black or white tubercles

Striations in the Taurus molecular cloud: Kelvin-Helmholtz instability or MHD waves?

The origin of striations aligned along the local magnetic field direction in the translucent envelope of the Taurus molecular cloud is examined with new observations of 12CO and 13CO J=2-1 emission obtained with the 10~m submillimeter telescope of the Arizona Radio Observatory. These data identify a periodic pattern of excess blue and redshifted emission that is responsible for the striations. For both 12CO and 13CO, spatial variations of the J=2-1 to J=1-0 line ratio are small and are not spatially correlated with the striation locations. A medium comprised of unresolved CO emitting substructures (cells) with a beam area filling factor less than unity at any velocity is required to explain the average line ratios and brightness temperatures. We propose that the striations result from the modulation of velocities and the beam filling factor of the cells as a result of either the Kelvin-Helmholtz instability or magnetosonic waves propagating through the envelope of the Taurus molecular cloud. Both processes are likely common features in molecular clouds that are sub-Alfvenic and may explain low column density, cirrus-like features similarly aligned with the magnetic field observed throughout the interstellar medium in far-infrared surveys of dust emission.Comment: 11 pages, 4 figures. Accepted for publication in MNRA

Magnetostrictive Neel ordering of the spin-5/2 ladder compound BaMn2O3: distortion-induced lifting of geometrical frustration

The crystal structure and the magnetism of BaMn$_2$O$_3$ have been studied by thermodynamic and by diffraction techniques using large single crystals and powders. BaMn$_2$O$_3$ is a realization of a $S = 5/2$ spin ladder as the magnetic interaction is dominant along 180$^\circ$ Mn-O-Mn bonds forming the legs and the rungs of a ladder. The temperature dependence of the magnetic susceptibility exhibits well-defined maxima for all directions proving the low-dimensional magnetic character in BaMn$_2$O$_3$. The susceptibility and powder neutron diffraction data, however, show that BaMn$_2$O$_3$ exhibits a transition to antiferromagnetic order at 184 K, in spite of a full frustration of the nearest-neighbor inter-ladder coupling in the orthorhombic high-temperature phase. This frustration is lifted by a remarkably strong monoclinic distortion which accompanies the magnetic transition.Comment: 9 pages, 8 figures, 2 tables; in V1 fig. 2 was included twice and fig. 4 was missing; this has been corrected in V