From: IN%"offiong@irg.usask.ca" "JJ Offiong" 13-NOV-1996 01:17:14.01 To: IN%"STEELE@DANSAS.USASK.CA" CC: Subj: RE: Please submit text for proposal sections Return-path: Received: from irg.usask.ca by DANSAS.USASK.CA (PMDF V5.0-6 #15020) id <01IBS27NM4ZK000LKQ@DANSAS.USASK.CA> for STEELE@DANSAS.USASK.CA; Wed, 13 Nov 1996 01:17:12 +0000 (GMT) Received: by irg.usask.ca from localhost (router,SLmailNT V2.0); Tue, 12 Nov 1996 19:17:06 -0800 (PST) Received: by irg.usask.ca from frey.usask.ca (128.233.17.27::mail daemon,SLmailNT V2.0); Tue, 12 Nov 1996 19:17:05 -0800 (PST) Date: Tue, 12 Nov 1996 19:17:04 -0600 From: JJ Offiong Subject: Re: Please submit text for proposal sections To: STEELE@DANSAS.USASK.CA Message-id: <19961112191706.0bf4e028.in@irg.usask.ca> Organization: University of Saskatchewan MIME-version: 1.0 X-Mailer: Pegasus Mail for Windows (v2.42a) Content-type: text/plain; charset=US-ASCII Content-transfer-encoding: 7BIT Priority: normal Comments: Authenticated sender is Hi David, Here is my submission for the proposal on absorption lines. It is basically a slightly re-worked version of the text file I gave to you previously. If you need anything else, do not hesitate to ask. J p.s. I noticed during your presentation last Wed, that you didn't have me listed on the ground based data handling team. I am on that team (just so you know...). **** Likelihood of Using Stellar Absorption Lines as Wavelength Markers for Spectra J Offiong It is well known that the spectra of many stars, i.e., those of certain spectral classes, on or not too far off the main sequence, resembles that of a blackbody. In addition to the Planck curve, there are a number of spectral features caused by absorption due to the stellar constituents. The absorption lines are often called Fraunhofer lines. In looking at the spectra of stars from various spectral classes over a large wavelength range "short lists" of absorption lines can be made. As an example, the spectral features of a solar type star (spectral class G68V) are given. Clearly evident by inspection in this spectrum are Calcium II H and K lines around 390 nm, the G-band which originates from CH absorption around 430nm, Magnesium I at 515nm and Sodium D near 580nm. The exact values of these quantities can be found in general literature (e.g., Allen: Astrophysical Quantities). The biggest difficulty will be the selection of lines. Ideally, suitable lines will be both strong and isolated. However, the currently proposed resolution of the instrument (about 5nm/pixel on the CCD) will limit the number of usable lines. Fortunately, at least for solar type stars, those listed above should prove strong and "wide" enough to be detectable on at least two to three pixels of the CCD. In order to use an absorption line as a wavelength marker, it will be necessary to determine the spectral type of the star from which the light came. This will require the matching of a measured spectrum to that of a well known spectrum. Traditionally, this has been done manually, however, recent advances in artificial neural networks has made automated spectral classification possible. This must be investigated in the future. Also to be determined is an appropriate "short lists" of usable absorption lines for different spectral types. In conclusion, it is appears that it will be possible to use absorption lines for wavelength markers. Adequate features exist that are of appropriate strength and width in the required wavelength range. Still, more precise work has yet to be done to determine exactly which lines will be detectable. Refrences: [1] Allen, C.W., Astrophysical Quantities, Oxford University Press Inc., N ew York, 1963. [2] Lehtinen, R., OSIRIS: A Technical Note on Level 1 Wavelength Calibration, 1996. __ "You're not going crazy, Arthur. You're going __ sane in a crazy world." - The Tick J Offiong Phone: (306)242-1972 E-Mail: