The interstellar C 18 O / C 17 O ratio in the solar neighbourhood : The ρ Oph cloud ⋆
نویسنده
چکیده
Observations of up to ten carbon monoxide (CO and isotopomers) transitions are presented to study the interstellar CO/CO ratio towards 21 positions in the nearby (d∼140 pc) low-mass star forming cloud ρ Oph. A map of the CO J=1–0 distribution of parts of the cloud is also shown. An average CO/CO isotopomeric ratio of 4.11 ± 0.14, reflecting the O/O isotope ratio, is derived from Large Velocity Gradient (LVG) calculations. From LTE column densities we derive a ratio of 4.17±0.26. These calculations also show that the kinetic temperature decreases from about 30 K in the cloud envelope to about 10 K in the cloud cores. This decrease is accompanied by an increase of the average molecular hydrogen density from 10 cm to >∼10 5 cm. Towards some lines of sight CO optical depths reach values of order unity.
منابع مشابه
Evaluation of the organophosphorus hydrolase enzyme activity in creams and investigation of its stability
The main purpose of this project is investigation of the organophosphorus hydrolase (OPH) enzyme activity in water in oil (w/o) and oil in water (o/w) creams and investigation of the OPH enzyme stability in formulated creams. OPH enzyme was extracted and purified from strain flavobacterium. The w/o and o/w creams were prepared using different formulations. In order to achieve an emulsion with m...
متن کاملThe Interstellar Rubidium Isotope Ratio toward Rho Ophiuchi A
The isotope ratio, Rb/Rb, places constraints on models of the nucleosynthesis of heavy elements, but there is no precise determination of the ratio for material beyond the Solar System. We report the first measurement of the interstellar Rb isotope ratio. Our measurement of the Rb I line at 7800 Å for the diffuse gas toward ρ Oph A yields a value of 1.21 ± 0.30 (1-σ) that differs significantly ...
متن کاملGalactic Chemical Evolution, Presolar Grains, and the Solar
Introduction: On the basis of radio measurements, it has been known for close to 30 years that the 18 O/ 17 O ratio is some 25% lower in the interstellar medium (ISM) than in the Solar System [1, 2]. Recent infrared observations of protostars confirm this low ratio in the local ISM [3]. Models of Galactic Chemical Evolution (GCE) have predicted that 18 O/ 17 O should remain constant as the Gala...
متن کاملLocal Interstellar Matter: The Apex Cloud
Several nearby individual low column density interstellar cloudlets have been identified previously based on kinematical features evident in high-resolution Ca observations near the Sun. One of these cloudlets, the ‘Apex Cloud” (AC), is within 5 pc of the Sun in the solar apex direction. The question of which interstellar cloud will constitute the next galactic environment of the Sun in princip...
متن کاملThe investigation on different light harvesting layers and their sufficient effect on the photovoltaic characteristics in dye sensitized solar cell
Titanium dioxide-based nanofibers (TiO2 nanofiber) were prepared by an electrospinning technique. The electrospun composite fibers were synthesized at different concentrations of titanium isopropoxide (25.35, 50.69, 76.05 wt%) and calcinated at different temperatures (450 oC, 650 oC and 850 oC) for 2 h. The diameters of nanofibers decreased by increas...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
دوره شماره
صفحات -
تاریخ انتشار 2004