The Tillinghast echelle is a crossdispersed echelle spectrograph using a Reticon detector. The photon-counting Reticon is a 2x936 pixel self-scanned photodiode array, coupled to a 3-stage image tube intensifier package, and then fed through the video amplifiers and electronics to the photon event discriminator, FIFO, and computer. The Reticon is cooled to about -40C from a Neslab chiller and re-circulating methanol bath.
The spectrograph has an internal Th-Ar lamp used for wavelength calibrations, and an internal incandescant lamp used for flat field exposures.
Only one echelle order is viewed by the reticon detector. The standard setting for our CfA programs and reduction routines is the order centered near 5187A, and covers a 50A bandpass. It is possible to set the spectrograph to view other orders, however the system efficiency is poor in the blue, and special arrangements for data reduction must be made with Dave Latham and Bob Davis.
The spectral resolution (R) is about 20,000 as measured from the spectra at 5177A. The 60" echelle yields radial velocity precisions of ~1km/sec. The spectrograph can be used to observe stars down to a magnitude of 13.0
The echelle grating is ruled at 79 lines per millimeter. We have 2 cross-dispersion gratings, a 300-line/mm and 1200-line/mm. The 300-line grating is used for the standard 5187 setup. The spectrograph slit is 80x500 microns, corresponding to ~1.5 arcsec by 9 arcsec on the sky.
The photon event discriminator and FIFO are located in the computer room, on the 60" equipment rack. The image intensifier and MCP controls are located on the north side of the telescope tube assembly.
The instrument exhibits significant flexure as the telescope is slewed to different parts of the sky. Therefore the slit plate is on a motorized stage that is controlled from the observing room. The slit postion is centered on the spectrograph order before beginning each observational sequence by balancing both halves of the reticon counts as displayed on the realtime system tcs. All stellar observations are preceded AND followed by a Th-Ar exposure (Th-Ar, star, Th-Ar). The power to the Th-Ar lamp and the sky/comp flip mirror are controlled by mechanical switches located on the observing desk.
The echelle has an easy-to-use "realtime system" interface that controls telescope pointing, detector control, and file names.
common commands used to take exposures and view data:
cex takes a 30-sec exposure named Th-Ar z "zgo;ret guide;fresh" starts and exposure, starts guider s "dmove;l+r;smooth 3;ep 0 1700" reads out buffer and displays lr "dmove; erase; lrplot 0 1700" reads and displays both sides of the reticon a "dmove;l-r;smooth 5;ep 0 1700" p "l+r;smooth 5;ep 0 1700" o "l+r;smooth 5;plot 0 1700" overplots file pcopy output current plot to printer sac "ret stop ; ret abort; ret clear; ret stop ; ret abort; ret clear" rfile x reads file #x comment pops up the comment editor for information stored in the file headers
To print ANY X window, make sure window is on top and do this: xwd -frame | xpr -device ps | lpr More mongo plot information
Open the dome (switch by door). Open all mirror doors (insure all covers are secured in open position). Note: See Dome instructions for complete operating and troubleshooting procedures.
Boot the TCS-PC if necessary. The 60" TCS program will automatically be loaded. See the TCS-PC users instructions.
Type "goechelle" on the SUN. In the dome, insert the TH-AR lamp and turn the rear switch "ON" and the front switch "OFF". Pull the dark-slide out and secure in place. Insure that the TH-AR lamp is functioning properly. Recommended procedure: Set lamp "ON" and mirror "ON" (in place). Type "cex" to start comparison exposure. View file using "show filenumber".
Boot the guide pc if necessary. Select ECHELLE. This program does more than autoguide for ECHELLE. It also controls the dome tracking, and sends counts to the hand-held terminal in the dome.. Toggle communications ON and turn dome tracking ON. With the telescope stowed, the dome should move to AZ = 90, and be open to due east.
Note: If guide PC is on, but only the DOS prompt ( c:\> ) is visible, just type "autoexec" and ENTER, then select "echguide" from menu to start the echelle guide program. See 60" Guider instructions for more information.
Note: The echelle autoguider does not work well with bright stars that have over 1000cps. Use "ret noguide" to turn off autoguider. Or do not turn the autoguider on when starting an exposure (use "zgo; fresh" instead of "z")
Make sure that the TCS RA and DEC indicators are solid blue, and NOT flashing red before turning on the rack. These indicators are located on the TCS-PC monitor. If the indicators are flashing red and not blue the telescope could run away! If the indicators are flashing red, hit F9 a few times on the TCS-PC keyboard. Turn on switch 2 (wait for delay), then 3, and 4 on front of rack located in chart room. See 60" Rack instructions for more information.
z - the most commonly used command to start an exposure. "z" is an alias for "zgo; fresh; ret guide" This will start an exposure, update the comments, and start the autoguider. During the exposure you will need to set the exposure time with "total x" or "mtotal y". At the end of the exposure the autoguider is automatically turned off. ret guide - will start the autoguider ret noguide - will turn off the autoguider (Note: it is not necessary to issue any guide commands directly from the guide pc. Autoguiding for the echelle is controlled though the rtshell window) cex - starts a comparison exposure (lamp "ON" and mirror "ON" before start of comparison exposure) comment - opens comment editor for updating comment fields dmove - reads out current working buffer into memory (data can then be plotted; see plot commands) dlink (arg) - link to directory "arg", "arg" can be 'now' for present directory, 'past' for yesterdays directory or yyyy/mm/dd to select directory by date. ep - erases present plot (if any) and diplays new plot ep n1 n2 - erase and plot from 'n1' to 'n2' are a range of pixels to be plotted. ex. ep 900 1200, plots portion from 900 to 1200 pixels erase - erases present plot fresh - use previous comments for new file goflat n - starts a 'n' second exposure named FLAT Note: goflat with no argument starts an infinite exposure and MUST be followed by a total command! l+r - adds left and right array counts l-r - subtracts right counts from left counts lrplot - plots left and right arrays separately mtotal m - starts an exposure for 'm' minutes. This can be used to end an infinite exposure which was started via "zgo" or "goflat" object obj - updates the object field to 'obj' plot n1 n2 - plot working buffer from pixels n1 to n2 rfile (num) - read or recover file number (num) +file (num) - add file (num) to working buffer. May be used to add two 20 minute exposures of object together for equivalent of 40 minute exposure. smooth n - smooths the desired plot 'n' times. zgo - starts an exposure of infinite length. Must stop this exposure with "mtotal m" or "total n" backup (-dat) - starts the backup routine. If no arg the backup is to the Exabyte 9mm tape drive. If -dat, backup uses the Dat 4mm tape drive. (use this in an xterm window). alias - gives entire list of aliases that already exist alias name - shows contents of alias 'name' if 'name' exists alias foo bar - create an alias foo that does bar. a single command needs no quotes ex. alias s ret stop multiple commands need quotes and separators (;) ex. alias sac "ret stop;ret abort;ret clear" NOTE: all aliases will be lost on exiting unless made permanent by adding to a rtrc file, ~/.echelle.rtrc for echelle.
a. switch comparison mirror "ON" (top switch on box next to console) b. set TH-AR switch "ON" (middle switch on box next to console) c. start a comparison exposure (type 'cex' and) d. when comparison is complete, turn both switches "OFF" e. at sunset, open dome shutters and mirror covers f. check RA and DEC indicators on the TCS display are steady blue g. turn rack on (switch 2 [wait for delay], then 3 and 4) h. set comparison mirror switch "ON" i. telescope remains at zenith (stow position) j. start an infinite exposure (type 'zgo' and ) k. momentarily turn the comparison mirror switch "OFF" and check the number of counts. This can be viewed on status display. WARNING - DO NOT turn comparison mirror "OFF" with a bright sky or the image tube can be damaged. Sky should be dark enough to have some stars visible. Counts should never exceed 20,000! l. edit the comment field (type 'object evesky' or 'comment' and enter "evesky" as the object name m. once counts drop to 10,000 they will begin dropping rapidly. n. when counts reach 5,500 - end the infinite exposure (zabort) do a 2 minute exposure (total 120) ex: zabort; total 120 do a comparison exposure (steps a thru d) slew telescope 3 hours west (+3 hours via the TCS window) do a comparison (steps a thru d) start a two minute exposure (total 120) update comment field with previous name (fresh) ex: total 120; fresh o. on TCS window - enter coordinates of object, or select catalog entry slew telescope to object insure object is correct (per finding charts) do a comparison exposure (steps a thru d) start an infinite exposure ex: z monitor counts using show until requested level is reached when it appears that enough counts will be reached by the next whole minute -- set the exposure time to end by next minute ex: mtotal m (m is total time, in minutes, from start [when z was entered] until the next whole minute) do a comparison exposure (steps a thru d) enter and slew to next object and repeat step s Note: the echelle autoguider does not work well with bright stars that have over 1000cps. Use "ret noguide" to turn off autoguider. p. just prior to sunrise, do the dawn sky - slew telescope 3 hours east (-3 hours via the TCS window) do a comparison exposure (steps a thru d) start an infinite exposure (zgo) when counts rise to 2500, end the infinite exposure and begin a 2 minute exposure ex: zabort; total 120 do a comparison exposure (steps a thru d) slew the telescope to zenith (stow position) do a comparison exposure (steps a thru d) start a 2 minute exposure (total 120) do a comparison exposure (steps a thru d) q. begin shutdown procedure: rack power off (switches 3 and 4 then switch 2) home dome on guide computer turn mirror switch "ON" close mirror covers close dome shutters turn guide camera high voltage and power "OFF" install incandescent lamp and turn "ON" BE SURE MIRROR SWITCH IS "ON" r. do three flats - (goflat 3600; repeat 2) s. insert dat tape in drive and type "backup -dat"