7 mm vla imaging of sio isotopic maser emission from source i … · >108 cm3 (humphreys et al.,...
TRANSCRIPT
J=10 (EVLA, ~5mas)v (GHz) Species 41791.9 30SiO v=2 42082.5 30SiO v=1 42287.9 29SiO v=2 42373.3 30SiO v=0 42519.4 28SiO v=3 42583.7 29SiO v=1 42820.6 28SiO v=2 42879.8 29SiO v=0 43122.1 28SiO v=1 43423.9 28SiO v=0
C. GODDI 1, L. GREENHILL 1, C. CHANDLER 2, E. HUMPHREYS 1, L. MATTHEWS 1, J. TAN 3 1HarvardSmithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138; 2National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801; 3Department of Astronomy, University of Florida, Gainesville, FL 32611
7 mm VLA imaging of SiO isotopic maser emission from Source I in Orion BN/KL7 mm VLA imaging of SiO isotopic maser emission from Source I in Orion BN/KL
7 mm spectral survey of Orion BN/KL with the GBT
7 mm VLA images of SiO (isotopic) masers in Orion BN/KL
Maser
Maser
Thermal wing Thermal wing
Abstract
v (GHz) Species 42373.3 30SiO v=0 D42519.4 28SiO v=3 U42820.6 28SiO v=2 D42879.8 29SiO v=0 D43122.1 28SiO v=1 D43423.9 28SiO v=0 D
Table 1: List of observed SiO J=10 lines
D=detected, U=undetected
Future prospects
Table 4: Optimum excitation conditions of SiO masers from the LVG pumping model from Humphreys et al. (Poster P.17)
Maser T (K) nH2
(cm3) Radii (AU)28SiO v=2 1000>2000 10911 1010028SiO v=1 10002000 10810 10100 28SiO v=0 > 600 <10 1001000 29SiO v=0 10002000 10810 10100 30SiO v=1 10002000 10810 10100
J=32 (ALMA, ~40 mas) v (GHz) Species 125372.9 30SiO v=2 126244.7 30SiO v=1 126860.8 29SiO v=2 127117.1 30SiO v=0127555.2 28SiO v=3 127748.3 29SiO v=1 128458.8 28SiO v=2 128636.7 29SiO v=0 129363.3 28SiO v=1 130268.6 28SiO v=0
Fig. 3: VLAB (~0.2'') map of SiO masers in Orion Source I. 29SiO and 30SiO masers (triangles and square with error bars) arise at a distance (10100
AU) from Source I (star) comparable to the v=1,2 emission (circles, crosses) Different maser species show similar global spatial/velocity distributions: red spots mostly
in the NW area, blue spots in the SE area, and systemic spots mainly towards the center 29SiO/30SiO masers tend to be excited where the 28SiO v=1,2 emission is weaker 28SiO v=0 emission (contour map) arises at large distances (~2001000 AU) from Source I
Observed Pairs (sub)array ('') (mJy) 30SiO v=0 + 28SiO v=2 EVLAB* 0.2 5 29SiO v=0 + 28SiO v=1 VLAB* 0.2 5 28SiO v=0 + 28SiO v=1 VLAB* 0.2 5
Table 3: VLA Observational Setup at 7 mm
*We used EVLA (13) and VLA (13) antennas as separate subarrays
Notes The grey font indicates lines undetected so far in BN/KL. The LVG pumping model predicts for 29SiO/30SiO Iv=1,2 v at T~1500 K and n
H2 >108 cm3 (Humphreys et al., Poster P.17),
making possible for the EVLA and ALMA the detection of isotopic emission from excited vstates.
Acknowledgments. The Very Large Array (VLA) of the National Radio Astronomy Observatory (NRAO) is a facility operated by the Association of Universities for Research in Astronomy, Inc. under cooperative agreement with the National Science Foundation.This work is supported by grant 0507478 from the National Science Foundation.
The high resolution VLA images provide for the first time a detailed description of the spatial and velocity distributions of SiO masers from different isotopologues (three) and vstates (two) around Orion Source I.
Key results regarding maser excitation are summarized below: The similar spatial and velocity distribution between 29SiO/30SiO v=0 and 28SiO
v=1,2 masers suggests that they are excited in the same gas reservoir at radii 10100 AU from Source I, whereas the 28SiO v=0 emission traces outflowing gas at larger distances (~2001000 AU) from Source I (Figs. 3).
Accordingly, the LVG pumping model by Humphreys et al. (Poster P.17) derives similar high temperatures and densities for the optimum excitation of both 29SiO/30SiO v=0 and 28SiO v=1,2 masers compared to 28SiO v=0 (Table 4).
The isotopes can also be weakly inverted at the lower temperature/densities required for the 28SiO v=0 excitation (see Poster P.17), consistent with the wing of emission in the v=0 profiles, detected by the GBT but resolved out by the VLA (Fig.2).
Excitation requirements for different species
The excitation conditions reported in Table 4 assume a ''classical'' radiativecollisional pumping. To model the SiO maser emission, however, one needs to take into account line overlaps among different transitions of SiO [2].High resolution imaging of SiO maser emission from different vstates and isotopes provides the key spatial information to constrain pumping models. Our data indicate that although the largescale distribution is similar for 28SiO v=1,2 and 29SiO/30SiO v=0 masers,their not complete spatial overlap implies nonlocal radiative effects should be incorporated in modeling the SiO maser emission [3,4].We plan to use a nonlocal spherical geometry radiative transfer code to model the SiO (isotopic) maser emission in Orion BN/KL.
Implications for future radiative transfer models
The capabilities of the EVLA and ALMA will significantly improve the understanding of I) SiO isotopic maser emission and II) the process of highmass star formation in Orion BN/KL.
I) The large instantaneous bandwidths (48 GHz) will allow the simultaneous observations of ten transitions in the J=10 (with the EVLA), J=21 and J=32(with ALMA) lines (Table 5), providing a nearly perfect astrometric registration among different masers. The number of transitions simultaneously observed is crucial to provide observational constraints to pump models. The improved angular resolution and sensitivity in addition will allow to measure more accurate positions and possibly detect weak features at large distance from Source I. II) A detailed study of SiO maser excitation will better constrain physical conditions in the circumstellar gas close to Source I. ALMA will measure accurate fluxes of the continuum emission from the central source up to 900 GHz, providing unique insights into the nature of the enigmatic Source I. The extremely richness of molecular line emission in Orion BN/KL (Fig. 1.) will allow ALMA to probe the dynamics and physical conditions of the circumstellar gas with unprecedented detail, separating the contributions from different YSOs in the SFR.
The promise of EVLA and ALMA
Orion BN/KL is the nearest known highmass star forming regions (SFR) and is known to exhibit a wide range of molecular and maser emission species. It is one of only three SFRs known to exhibit emission from SiO masers [1] and the only one that contains all known SiO isotopic species. Imaging with the Very Large Array (VLA) and the Very Long Baseline Array (VLBA) shows that SiO v=1,2 emission arises in the proximity (radii of 2070 AU) of the highmass young stellar object (YSO) Radio Source I, whereas SiO v=0 emission is distributed at larger distances (~2001000 AU) in a bipolar outflow (see Poster P.17 from Humphreys et al.).
In a GBT survey of Orion BN/KL at 7 mm, we detected for the first time the v=0 J=10 line from 29SiO and 30SiO. We then used the VLA to image five transitions from three SiO isotopologues (Table 1), which allowed us to establish the maser nature and the location of the 29SiO and 30SiO emission within 100 AU from Source I. The presence of maser emission from two vibrationally excited transitions and three isotopologues from SiO makes Orion Source I in BN/KL a good cosmic laboratory for studying the poorly characterized excitation mechanisms of (isotopic) SiO masers.
Future joint studies with the EVLA and ALMA will significantly extend this work by covering the J=10, J=21, and J=32 transitions, greatly broadening the foundation for pump models.
Fig. 2: Spectra of 28SiO v=0,1,2 J=10 and 29SiO and 30SiO v=0 J=10 from Orion BN/KL observed with the GBT and the VLA. Multiple transitions show similar doublepeaked profiles and velocity extent. Less than 30% of the GBT emission has been recovered in the VLA maps for
29SiO and 30SiO. Wing emission is also present in all the GBT v=0 profiles. Both elements indicate the presence of a thermal component filtered out by the VLA.
Brightness temperatures of ~3103 K are inferred for the strongest 29SiO and30SiO components, attesting to maser emission.
References[1] Zapata, L.A., Leurini, S., Menten, K. M., Schilke, P., Rolffs, R., & Hieret, C. 2008, AJ, 136, 1455 [2] GonzalezAlfonso, E., & Cernicharo, J. 1997, A&A, 322, 938[3] Baudry, A., Herpin, F., & Lucas, R. 1998, A&A, 335, 654 [4] Herpin, F. & Baudry, A. 2000,A&A, 359, 1117
J=21 (ALMA, ~25 mas) v (GHz) Species 83583.0 30SiO v=2 84164.3 30SiO v=184575.0 29SiO v=2 84745.9 30SiO v=0 85038.0 28SiO v=3 85166.7 29SiO v=1 85640.4 28SiO v=2 85759.0 29SiO v=0 86243.4 28SiO v=1 86847.0 28SiO v=0
Table 5: List of SiO transitions simultaneously observable with the EVLA and ALMA
Table 2: Detected Molecular Species In Orion BN/KL with the GBT at 7 mm
Fig. 1. Line survey of Orion BN/KL at 7 mm (Nov 2007). We report the first detection of 29SiO and 30SiO v=0 J=10. We found also indication of the presence of rare long cchain molecules, HC5N and HC7N. Future sensitive observations at higher frequencies with ALMA would be crucial for unambiguous identifications of these long cchain species.