1. 3-D SUBMILLIMETER SPECTROSCOPY FOR ASTROPHYSICS AND SPECTRAL ASSIGNMENT SARA FORTMAN, CHRISTOPHER NEESE, IVAN R. MEDVEDEV, FRANK C. DE LUCIA, Department of Physics, The Ohio State University, Columbus, OH 43210-1106, USA. Midwest Astrochemistry Meeting Urbana, IL November 8 th, 2008

2. 3456897 Herschel High BandHerschel Low Band 0200100080060040012001400160018002000 Too Many Weeds Frequency/GHz 1 mm Survey of Orion with IRAM 30-m Telescope Class 1 Weeds Methanol – CH 3 OH Methyl Formate – HCOOCH 3 Dimethyl Ether – CH 3 OCH 3 Ethyl Cyanide – CH 3 CH 2 CN Class 2 Weeds Vinyl Cyanide – C 2 H 3 CN Sulfur Dioxide – SO 2 Methyl Cyanide – CH 3 CN Cyanoacetylene – HC 3 N Acetaldehyde – CH 3 CHO The consensus is that most of the unknown lines come from these molecules and their isotopologues. The challenge becomes solving this problem in the context of ALMA’s great sensitivity and Herschel’s new spectral regions. courtesy of J. Cernicharo

3. Ethyl Cyanide at 300K

4. Ethyl Cyanide as a Function of Temperature If you want an intensity in our temperature range, we know it. This temperature range is too high for most astronomical spectra. We can use collisional cooling to reach lower temperatures.

5. Ratios to Obtain Lower State Energy We can plot the log of the ratio in log(1/T) space and expect to see a straight line. Consider taking the ratio of two lines of which one is assigned and the other is unassigned. We could extrapolate to low temperatures, but this will give large errors. We want to determine the lower state energies in order to create a catalogue.

6. Lower State Energy vs. Thermal Behavior

7. InSb detector Aluminum cell: length 6 m; diameter 15 cm Lens Path of microwave radiation Preamplifier Glass rings used to suppress reflections Data acquisition system Computer Thermal enclosure Agilent Synthesizer Submillimeter Spectrometer VDI Lens

8. Temperature Control Temperature Range: 228 – 405 K (-45 – 132 °C) at ~.8 degrees/min Take 350 scans over 4 hours with the solid state system Take a scan every 38.7 seconds

9. Recent Results SO 2 160 total lines 60 reference lines Temperature Range: 234 – 403 K (-39 – 131 °C) Standard deviation: 21.9 cm^-1 C 2 H 5 CN 1645 total lines 405 reference lines. Range: 234 – 389 K (-39 – 116 °C) Standard deviation of known lines: ~50 cm^-1 Took sulfur dioxide (SO 2 ) and ethyl cyanide (C 2 H 5 CN) spectra from 570 – 650 GHz Calculated the lower state energy of all lines by taking ratios with a subset of the known lines Assumed the lower state energy is the average of the energies calculated from the subset of known lines Checked the results of the known lines

10. Summary The Problem There are too many weed lines for the traditional assignment method of spectroscopy. A Solution Intensity calibrated complete spectra over the ALMA and Herschel Bands by –Direct measurement at astrophysical temperatures and/or –Lower state energy / Einstein coefficient modeling for catalogues. The error in the predicted intensities of the interpolated spectra is comparable to the error in experimental intensity measurements.

11. Ethyl Cyanide as a Function of Temperature

12. Sulfur Dioxide as a Function of Temperature

13. Astronomy The smallest errors in intensities will come when the calculated temperature is bounded by experimental temperatures The error in the predicted intensity will be of the order the error in the observations (or better because we make many observations). Propagation of Error and Uncertainties Spectroscopy We expect to reduce uncertainties by a factor of 10 by: Replacing the peak finder with analysis Fitting a model to the baseline ripple Using a grand fit of all assigned lines as the reference line instead of a single line Getting a proper average over the ends by using the spectroscopic temperature Operating over a larger temperature range (using a collisional cooling cell to 2K)

14. Graphing in Two and Three Dimensions Frequency (MHz) Intensity (nm2*MHz) Lower State Energy (cm-1) 1629775.1963711631.1015 16311917.025509113.2438 1635685.0442872400.8251 16360637.16208665.264397 1639254.3062572488.5152 Traditional approach uses a 2D (intensity vs. frequency) plot New approach creates a 3D plot from the intensity, frequency and lower state energy data

15. Two Related Objectives Spectroscopy Challenge Bootstrap Assignment in Complex Spectra FASSST spectra may contain >10^5 lines in many vibrational states Traditional Approach Use 2D (intensity, frequency) spectra to assign and bootstrap in each vibrational state New Approach Observe intensity calibrated variable temperature spectrum and calculate lower state energies. Use intensity, frequency and lower state energies in the bootstrap assignment Astronomy Challenge Current telescopes approach confusion limit Many unassigned lines New systems (Alma, Herschel) will be more powerful Traditional Approach Quantum Mechanical predictions of astrophysical spectra give intensity and frequency as a function of temperature Spectroscopists calculate and fit what we can, not what astronomers need New Approach Predict intensity and frequency as a function of temperature without assignment courtesy of J. Cernicharo Intensity Calibrated Variable Temperature Spectroscopy Observe 2D spectra at many temperatures Calculate intensity, frequency and lower state energies for assigned and unassigned lines Give astronomers what they want Give spectroscopists more information