A Search For Interstellar Urea

With CARMA

Hsin-Lun Kuo, Lewis Snyder, Douglas Friedel, Leslie Looney,

Benjamin McCall (UIUC),

Anthony Remijan (NRAO), Frank Lovas (NIST), Jan Hollis

(NASA)

Motivation

Urea (NH2)2CO has measured and calculated laboratory frequencies good to a few kHz.

In preparation of CARMA search for protonated methanol (frequencies measured by McCall group), we wish to develop procedures with trustworthy calibrator fluxes, proper baseline subtraction, and self calibration to extract weak emission lines from CARMA data.

CARMA (Combined Array for Research in Millimeter-wave Astronomy)

Owens Valley Radio Observatory (OVRO) -- 10.4 m X6

Berkeley-Illinois-Maryland Association (BIMA) -- 6.1 m X9 105 baselines Angular resolution about 0.3", 0.8", 2", 5", or 10" at 100

GHz in A, B, C, D, and E configuration Operates at 3 mm (85-116 GHz) and 1 mm (215-270

GHz)

Urea LinesFrequency(GHz) Q.N. Frequency(GHz) Q.N.

85.082429(7) 4(4,1)-3(3,0) 211.077808(31) 18(*,17)-17(*,16)

91.936572(9) 7(*,6)-6(*,5) 211.177686(45) 19(*,19)-18(*,18)

92.031813(11) 8(*,8)-7(*,7) 221.907450(37) 19(*,18)-18(*,17)

102.767529(10) 8(1,7)-7(2,6) 222.007452(53) 20(*,20)-19(*,19)

102.767550(10) 8(2,7)-7(1,6) 232.736742(44) 20(*,19)-19(*,18)

102.864309(11) 9(*,9)-8(*,8) 232.836861(63) 21(*,21)-20(*,20)

108.265140(9) 5(5,1)-4(4,0) 243.565664(53) 21(*,20)-20(*,19)

112.023887(9) 5(5,0)-4(4,1) 243.665896(74) 22(*,22)-21(*,21)

254.394200(62) 22(*,21)-21(*,20)

254.494539(86) 23(*,23)-22(*,22)

265.222330(73) 23(*,22)-22(*,21)

265.322772(99) 24(*,24)-23(*,23)

Urea Energy Levels

Continuum Map of Sgr B2 (N)

Urea 1mm Spectra

Line Fits & Spectral Analysis

Beam averaged total number density (cross-correlation array)

(See Appendix in Snyder et al. 2005)

Intensity ratio

€

N tot =Idv∫

Bθa ×θb

QrotSμ 2ν 3

eEu /T × 2.04 ×1020cm−2

€

I1I2

=B1θa1 ×θb1B2θa2 ×θb2

⎛

⎝ ⎜

⎞

⎠ ⎟S1

S2

⎛

⎝ ⎜

⎞

⎠ ⎟ν 1

3

ν 23

⎛

⎝ ⎜

⎞

⎠ ⎟eEu 2 −Eu1

T

Temperature Plots

Plot I1 v.s. Trot

All plots consistent with Trot ~ 80 K

Previous BIMA result Trot = 77 K

€

I1 = I2B1θa1 ×θb1B2θa2 ×θb2

⎛

⎝ ⎜

⎞

⎠ ⎟S1

S2

⎛

⎝ ⎜

⎞

⎠ ⎟ν 1

3

ν 23

⎛

⎝ ⎜

⎞

⎠ ⎟eEu 2 −Eu1

T

Urea 1mm Spectra

Urea 3mm Spectra

Conclusion

Rotational temperature Trot ~ 80K Linewidth ∆v ~ 2.05 km s-1

Beam-averaged total column density Ntot = 9.75 1014 cm-2

Proper coupling of source size to the beam size is essential for flux measurements and detection limits; it helps bring out weak signals that are otherwise blended with extended emission.