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Masers Surveys with Mopra: Which is best 7 or 3 mm? Simon Ellingsen, Maxim Voronkov & Shari Breen. 3 November 2008. Overview. What maser transitions lie in the 7 and 3 mm frequency bands? What science could be done with large-scale surveys in these transitions? - PowerPoint PPT Presentation
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Masers Surveys with Mopra: Which is best 7 or 3 mm?
Simon Ellingsen, Maxim Voronkov & Shari Breen
3 November 2008
Maser Surveys with Mopra: Which is best 7 or 3 mm?
Overview
• What maser transitions lie in the 7 and
3 mm frequency bands?
• What science could be done with large-
scale surveys in these transitions?
• The optimal maser configuration.
• What sensitivity is required?
Maser Surveys with Mopra: Which is best 7 or 3 mm?
Masers at millimetre wavelengths
• Most of the strong, well studied maser transitions are at centimetre wavelengths - why?
• At higher frequencies the number of maser transitions increases, but they are typically less intense and less common than those at centimetre wavelengths.
• In both the 7 and 3 mm bands the dominant maser transitions are SiO from late-type stars and class I methanol masers.
• The class I methanol masers trace outflows and are quite distinct from the better studied 6.7 GHz (class II) masers.
Maser Surveys with Mopra: Which is best 7 or 3 mm?
Masers in the 7 mm bandFrequency
(GHz)Molecule/Type Comments
36.17Methanol (class I)
Common, strong
37.70, 38.29, 38.45
Methanol (class II)
Rare, weak
42.37 - 43.12SiO (late-type
stars)Common,
strong
44.07Methanol (class I)
Common, strong
Maser Surveys with Mopra: Which is best 7 or 3 mm?
Masers in the 3 mm bandFrequency
(GHz)Molecule/Type Comments
84.52, 95.17Methanol (class I)
Common, strong
86.14 - 86.85SiO (late-type
stars)Common,
strong
89.07HCN (late-type
stars)Weak, rare
86.2, 86.6, 86.9, 107.01,
108.0
Methanol (class II)
Weak, rare Intermediate
Maser Surveys with Mopra: Which is best 7 or 3 mm?
Class I methanol masers - poor cousins
• Methanol maser transitions are empirically divided into two classes on the basis of where they arise.
• Class II methanol masers are associated with high-mass star formation regions. They are typically found close to IR sources, OH and water masers (e.g. 6.7, 12.2 GHz).
• Class I methanol masers are associated with interactions between outflows and molecular gas, they are offset from IR sources and other types of masers (e.g. 36, 44, 95 GHz).
• Theoretically the empirical difference arises from different pumping schemes - collisional for class I, radiative for class II.
Maser Surveys with Mopra: Which is best 7 or 3 mm?
Maser Surveys with Mopra: Which is best 7 or 3 mm?
Class I methanol masers - poor cousins
• Methanol maser transitions are empirically divided into two classes on the basis of where they arise.
• Class II methanol masers are associated with high-mass star formation regions. They are typically found close to IR sources, OH and water masers (e.g. 6.7, 12.2 GHz).
• Class I methanol masers are associated with interactions between outflows and molecular gas, they are offset from IR sources and other types of masers (e.g. 36, 44, 95 GHz).
• Theoretically the empirical difference arises from different pumping schemes - collisional for class I, radiative for class II.
Maser Surveys with Mopra: Which is best 7 or 3 mm?
Science with Class I masers
• The association of class I methanol masers with outflows has led to the suggestion that they may trace a very early stage of high-mass star formation.
• There are no substantial, sensitive unbiased searches for class I masers. The best targeting strategy is to search towards known class II methanol masers (Ellingsen 2005).
• It appears that some class I masers are associated with lower-mass star formation (Kalenskii et al. 2006).
• They are potentially powerful probes of the physical conditions at multiple locations in the star forming region.
Maser Surveys with Mopra: Which is best 7 or 3 mm?
Class I in IRAS16547-4247
Red contours = 25 GHz continuum
Yellow contours = 95 GHz class I
Colour image = Shock-excited H2
(Voronkov et al. 2006)
Maser Surveys with Mopra: Which is best 7 or 3 mm?
SiO - Probing Galactic dynamics
• Searches for OH/IR stars at 1612 MHz have previously been used to study Galactic structure (Sevenster, Chapman, Habing et al.)
• More than 2000 SiO masers are now known, primarily in the Northern hemisphere and from targeted searches (Deguchi et al. 2004)
• In addition to Galactic structure SiO masers can be used to investigate stellar evolution, stellar mergers, open star and globular clusters.
Maser Surveys with Mopra: Which is best 7 or 3 mm?
Galactic Distribution of SiO Masers(Deguchi et al. 2007)
Maser Surveys with Mopra: Which is best 7 or 3 mm?
SiO - Probing Galactic dynamics
• Searches for OH/IR stars at 1612 MHz have previously been used to study Galactic structure (Sevenster, Chapman, Habing et al.)
• More than 2000 SiO masers are now known, primarily in the Northern hemisphere and from targeted searches (Deguchi et al. 2004)
• In addition to Galactic structure SiO masers can be used to investigate stellar evolution, stellar mergers, open star and globular clusters.
Maser Surveys with Mopra: Which is best 7 or 3 mm?
95 GHz Class I Methanol in the DQS
• The DQS CS observations included the 95 GHz class I methanol maser transition in the band.
• The DQS observations (zoom mode) had TRMS ~ 0.2-0.3 K at the maser frequency.
• There are two previously known masers in the region covered, one of which was detected.
• This suggests that there would be around 3 detections per sq. degree at this sensitivity.
Maser Surveys with Mopra: Which is best 7 or 3 mm?
95 GHz class I methanol masers in the DQS
(cube courtesy of Nadia Lo)
Known source Possible New Detection
Maser Surveys with Mopra: Which is best 7 or 3 mm?
95 GHz Class I Methanol in the DQS
• The DQS CS observations included the 95 GHz class I methanol maser transition in the band.
• The DQS observations (zoom mode) had TRMS ~ 0.2-0.3 K at the maser frequency.
• There are two previously known masers in the region covered, one of which was detected.
• This suggests that there would be around 3 detections per sq. degree at this sensitivity.
Maser Surveys with Mopra: Which is best 7 or 3 mm?
The Best Option for Masers• The best maser science would be achieved from a sensitive
search for class I methanol and SiO masers.• The best wavelength range in which to do this is the 7mm
band (both system performance and maser intensity are better there).
• With 42-50 GHz frequency setup you get multiple SiO transitions, class I methanol, thermal methanol at 48 GHz, CS(1-0) + isotopes, HCCCN, CCS.
• Zoom mode gives approximately 900 km/s velocity coverage at 0.21 km/s resolution for up to 16 sub-bands.
• Using the ‘strawman’ 7mm survey specifications and CMZ results as a guide we would expect TRMS = 0.12 K (1 pass)
Maser Surveys with Mopra: Which is best 7 or 3 mm?
Does the Strawman stand up?• Deguchi et al. (2004) surveyed 400 colour-selected IRAS
sources and detected 254 SiO masers in the 43 GHz lines (RMS ~0.07 K).
• A 1-pass Mopra survey would detect 37% of the Nobeyama sources and a 2-pass survey would detect 51%.
• Targeted 44 GHz class I methanol maser (Slysh et al. 1994 & Kurtz et al. 2004) suggest a similar scenario for those.
• Assuming the SiO and class I masers show similar flux density distributions, I estimate approximately 20 class I maser detections and a similar number of SiO per sq deg.
• A 2-pass strawman survey is 3.1 years of telescope time to cover 90 sq degrees (HOPS)
Maser Surveys with Mopra: Which is best 7 or 3 mm?
Maser Surveys with Mopra: Which is best 7 or 3 mm?
Does the Strawman stand up?• Deguchi et al. (2004) surveyed 400 colour-selected IRAS
sources and detected 254 SiO masers in the 43 GHz lines (RMS ~0.07 K).
• A 1-pass Mopra survey would detect 37% of the Nobeyama sources and a 2-pass survey would detect 51%.
• Targeted 44 GHz class I methanol maser (Slysh et al. 1994 & Kurtz et al. 2004) suggest a similar scenario for those.
• Assuming the SiO and class I masers show similar flux density distrubutions, I estimate approximately 20 class I maser detections and a similar number of SiO per sq deg.
• A 2-pass strawman survey is 3.1 years of telescope time to cover 90 sq degrees (HOPS)
Maser Surveys with Mopra: Which is best 7 or 3 mm?
Thermal + Masers = Complementary
• Masers are good at signposting interesting regions (e.g. young star formation regions, outflows etc) and can be used to measure kinematics.
• The masers trace “special” conditions, but generally it is easier and more reliable to use thermal lines to estimate important physical parameters (temperature, density etc).
• Thermal observations at the maser locations are critical to better understanding the star formation and/or outflow physics (as well as how the masers are produced).
• Thermal methanol can measure the temperature, CS traces the dense gas, thermal SiO the outflows etc.
Maser Surveys with Mopra: Which is best 7 or 3 mm?
Kalenskii et al. (2007):
Rotation diagrams from 96.7 GHz series of methanol (similar to 48 GHz series).
Multiple series gives better constraints.
Maser Surveys with Mopra: Which is best 7 or 3 mm?
ATCA + CABB better for masers?
• To determine associations and make the most of any science from maser surveys requires accurate positions for the masers => ATCA observations of the detections.
• The ATCA achieves the same sensitivity as the Mopra Strawman 7mm survey in 10 seconds onsource.
• The ATCA could potentially observe 0.1 sq deg per hour (onsource), but a practical implementation with current limitations probably requires a factor of several slower.
• With CABB it would be possible to simultaneously observe the SiO, Class I methanol and continuum (hypercompact HII region search).
Maser Surveys with Mopra: Which is best 7 or 3 mm?
Mopra observations (Maxim Voronkov) of 36 GHz class I methanol masers in the low-mass star forming region BHR71.
Maser Surveys with Mopra: Which is best 7 or 3 mm?
Conclusions• The requirements of maser and thermal
surveys are not particularly compatible:– At 7mm the masers are stronger, but the
thermal lines are weaker and less prevalent.– At 3mm the masers are weaker, the system is
worse, achieving worthwhile sensitivity very difficult.
• A smaller-scale maser survey (with the ATCA) of part of the Mopra survey region may yield the best science.