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Proposal Identification No.:

A2769 Arecibo Observatory

Date Received: 2012-Aug-30 15:06:14 William E. Gordon Telescope Observing Time Request COVER SHEET

Section I - General Information
Submitted for Sep 1 2012. This proposal has not been submitted before. Proposal Type: General Category: Sub-Category: Observation Category: Time Requested this semester: Hours already used for this pro ject: Additional Hours required to complete pro ject: Minimum Useful Time: Expected Data Storage: Prop osal Title: ABSTRACT: Regular Astronomy Spectroscopy Galactic 80

1 hour less than 100 GB

True HI column density of five ma jor giant molecular clouds

We showed in Lee et al. that the HI surface density of the atomic envelope associated with the Perseus molecular cloud is relatively constant. This could be explained with the equilibrium model for H2 formation whereby the observed HI saturation represents the shielding column necessary for the transition from atomic to molecular medium. However, an alternative explanation is the existence of high optical depth HI. While we have shown that this explanation does not hold in the case of Perseus, it is essential to investigate other Giant Molecular Clouds (GMCs) at different stages of chemical evolution. We are now investigating five GMCs covered by the GALFA-HI survey. To estimate the importance of the high optical depth HI we propose HI absorption observations in the direction of 80 radio continuum sources located behind these GMCs. We will derive the correction needed for the high HI column density and compare our findings with predictions from equilibrium and turbulent models. Outreach Abstract: Understanding how molecules the process of star formation. the Milky Way using the high our observations with several form out of the diffuse atomic medium is a key step toward understanding We are investigating the transition between atomic and molecular gas in sensitivity and resolution of the Arecibo radio telescope, and by comparing theoretical predictions.

Name Snezana Stanimirovic Min-Young Lee

Institution UW-Madison UW-Madison

E-mail sstanimi@astro.wisc.edu lee@astro.wisc.edu

Phone 6088901458

Student no G

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Additional Authors
Claire Murray, UW-Madison graduate student; cmurray@astro.wisc.edu Carl Heiles, UC-Berkeley; heiles@astro.wisc.edu

This work is not part of a thesis.

Remote Observing Request

Observer will travel to AO X Remote Observing In Absentia (instructions to operator)

Section I I - Time Request
The following times are in LST. For these observations night-time is not needed.

Begin ­ End Interval­Interval 03:20 ­ 05:45 03:20 ­ 05:19 05:45 ­ 07:15 05:20 ­ 07:30

Days Needed at This Interval 10 10 20 10

Time Constraints (Must Be Justified in the Prop osal Text)

Section I I I - Instruments Needed
L-wide Atmospheric Observation Instruments:

Sp ecial Equipment or setup:

none

Section IV - RFI Considerations
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Frequency Ranges Planned
1420-1720 This proposal requires Iridium RFI protection at 1612 MHz between 10pm and 6am EST.

Section V - Observing List Target List
Taurus RA=04:00 to California RA=03:45 Rosette RA=05:45 to Mon OB1 RA=05:45 05:18, Dec=21 to 31deg to 05:00, Dec=28 to 38deg 07:15, Dec=0.5 to 10deg to 07:15, Dec=5 to 15deg

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