4,010 research outputs found
Detection of 84-GHz class I methanol maser emission towards NGC 253
We have investigated the central region of NGC 253 for the presence of
84.5-GHz (E) methanol emission using the Australia
Telescope Compact Array. We present the second detection of 84.5-GHz class~I
methanol maser emission outside the Milky Way. This maser emission is offset
from dynamical centre of NGC 253, in a region with previously detected emission
from class~I maser transitions (36.2-GHz E and 44.1-GHz
A methanol lines) . The emission features a narrow
linewidth (12 km s) with a luminosity approximately 5 orders of
magnitude higher than typical Galactic sources. We determine an integrated line
intensity ratio of between the 36.2 GHz and 84.5-GHz class I
methanol maser emission, which is similar to the ratio observed towards
Galactic sources. The three methanol maser transitions observed toward NGC 253
each show a different distribution, suggesting differing physical conditions
between the maser sites and that observations of additional class~I methanol
transitions will facilitate investigations of the maser pumping regime.Comment: Accepted into ApJL 12 October 2018. 10 pages, 3 Figures and 2 Table
37 GHz methanol masers : Horsemen of the Apocalypse for the class II methanol maser phase?
We report the results of a search for class II methanol masers at 37.7, 38.3
and 38.5 GHz towards a sample of 70 high-mass star formation regions. We
primarily searched towards regions known to show emission either from the 107
GHz class II methanol maser transition, or from the 6.035 GHz excited OH
transition. We detected maser emission from 13 sources in the 37.7 GHz
transition, eight of these being new detections. We detected maser emission
from three sources in the 38 GHz transitions, one of which is a new detection.
We find that 37.7 GHz methanol masers are only associated with the most
luminous 6.7 and 12.2 GHz methanol maser sources, which in turn are
hypothesised to be the oldest class II methanol sources. We suggest that the
37.7 GHz methanol masers are associated with a brief evolutionary phase (of
1000-4000 years) prior to the cessation of class II methanol maser activity in
the associated high-mass star formation region.Comment: 14 pages, 4 figures, accepted for publication in Ap
Simultaneous interplanetary scintillation and Heliospheric Imager observations of a coronal mass ejection
We describe simultaneous Interplanetary Scintillation (IPS) and STEREO Heliospheric Imager (HI) observations of a coronal mass ejection (CME) on 16 May 2007. Strong CME signatures were present throughout the IPS observation. The IPS raypath lay within the field-of-view of HI-1 on STEREO-A and comparison of the observations shows that the IPS measurements came from a region within a faint CME front observed by HI-1A. This front may represent the merging of two converging CMEs. Plane-of-sky velocity estimates based on time-height plots of the two converging CME structures were 325 kms?1 and 550 kms?1 for the leading and trailing fronts respectively. The plane-of-sky velocities determined from IPS ranged from 420 ± 10 kms?1 to 520 ± 20 kms?1. IPS results reveal the presence of micro-structure within the CME front which may represent interaction between the two separate CME events. This is the first time that it has been possible to interpret IPS observations of small-scale structure within an interplanetary CME in terms of the global structure of the event
Transients influencing rocket engine ignition and popping Interim report
Engine design and operating parameters studied for effects on rocket engine ignition and poppin
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