MIKE User Manual
Local copy of the MIKE User’s Manual
Rebecca Bernstein, Steve Shectman, Steve Gunnels, Ian Thompson, Greg Burley, Christoph Birk, Stefan Mochnacki, Alex Athey
This manual contains the basic information needed to observe with MIKE. The instrument is described in more detail in Bernstein, Shectman, Gunnels, Mochnacki, Athey 2002, Proc SPIE 4841
MIKE is a double echelle spectrograph. The first optical element in the spectrograph is a dichroic which reflects (transmits) light into the blue (red) arms of the spectrograph. Each side has its own shutter and CCD, so the two sides can be used simultaneously with independent exposure times. The basic specifications of each side are listed in the table below. The parameters which the observer can select are exact wavelength coverage and the slit width.
The spectrograph delivers full wavelength coverage from about 3350-5000Å (blue) and 4900-9500Å (red) in its standard configuration. This configuration is set by the cross over wavelength of the dichroic (4950Å). As the observer, you can choose to have the grating angle adjusted to select a different set of orders to go bluer on the blue side (down to 3200A) or redder on the red side (up to 10,000Å). But it is not possible to use a different dichroic, gratings, or prisms. These elements are permanent.
Because MIKE uses prisms for cross dispersion, the separation between orders changes as a function of wavelength. The smallest separation is about 6″. The longest slit that can be used for full wavelength coverage is therefore 5″ long. Several different slit widths are available, as discussed below. Choose a slit width that gives you the resolution you want.
A small blue box in the control room allows the observer to remotely control internal lamps (ThAr and incandescent), the slit position, and the focus of the cameras. The first time user should let the Instrument Specialist focus the spectrograph.
The CCDs and their electronics were provided and are maintained by Ian Thompson and Greg Burley. All information related to upgrades, linearity, and detailed behavior has been provided by Ian Thompson. MIKE also has a fiber system which was built by Mario Mateo (UM) and Alex Athey (UM, OCIW). The fiber-fed mode is not yet available for use by guest observers without explicit permission and assistance from Mateo.
1- Ian Thompson reports that he has fixed the linearity problems associated with the blue side CCD (Lincoln Labs, installed May 2004). Any data taken after September 20, 2005 should be linear to digital saturation of the A/D converter.
1- A new dichroic was installed which has a crossover wavelength of ~495 nm. (The old dichroic produced a crossover wavelength of ~455nm.)
2- A Lincoln Labs CCD was installed on the blue side. Like the original, this CCD has 2k x 4k x 15 micron pixels. On the plus side, it has very high quantum efficiency. On the minus side, it has limited dynamic range. This is discussed further in Section 4 (“Efficiency and Exposure Times”), below. The bottom line is that you should keep the total count levels in your data below 8,000 DN per physical pixel (1×1 binning), and below 16,000 DN at any binning. [As of October 2005, this problem has been fixed, as noted above.]
|Blue Side||Red Side|
|effective focal ratio||f/3.9||f/3.6|
|scale at CCD||8.2 pix/” (0.12″/pix)||7.5 pix/” (0.13″/pix)|
|detector||2048×4096 (15μm pix)||2048×4096 (15μm pix)|
|gain||~0.47 e-/DN||~1.0 e-/DN|
|Read noise||~2 e-/pix||~3.5 e-/pix|
|Dark current||~5 DN/pix/hr||~2 DN/pix/hr|
|Resolution (0.35″ slit)||83,000||65,000|
|Resolution (1.0″ slit)||28,000||22,000|
|Prism (cross-disperser)||Fused Silica (2 prisms)||PBM2 (1 prism)|
*The grating position and wavelength ranges for the standard setup are given in Section 8
4. Resolution and binning:
The cameras make very good images and can easily resolve a 0.35″ slit (the smallest slit available). That means that the number of pixels per resolution element of your spectra will be limited only by the slit width you use (smaller slits mean higher resolution, linearly related). If you are observing very faint objects, it pays to bin the data in the spectral and spatial directions.
The scale of the CCD detectors is about 8.2 pixels/” (blue side) and 7.5 pixels/” (red side). So if you are using a slit which is wider than 0.5″ there is not much point in taking unbinned data. In other words, you should bin in the spectral (y) direction so that slit width is Nyquist sampled. In addition to significant gains in readout time, your data will be less effected by readnoise, which does not increase significantly with binning. It is very common to use MIKE binned 2×2 or 3×2 on both sides.
5. Efficiency and Exposure Times:
The plot below shows the source flux (in AB mag) from which we detect 1 e-/sec/A. The slit-to-detector efficiency is roughly 37% (~4500Å ) on the blue side and 20% (~6500Å ) on the red side. (Measurement and calibration courtesy of Scott Burles and Kristin Burgess, MIT.)
This plot is based on data taken through a 2″ slit in 0.7″ seeing, so not much light was lost at the slit. If you use a slit width which is matched to the seeing (1″ slit in 1″ seeing), you should expect to lose about 25% of the light at the slit.
This plot is all you need to estimate the exposure times for your program.
To be clear, here is an example of how to use this plot:
Flux of target star: V=15 mag
Desired SNR: 50 per pixel (i.e. ~ 2500 e-/pixel)
# Angstroms/pixel: 0.05 Å /pixel red side, w/o binning in spectral direction (y)
seeing, slit, airmass: seeing=0.8″ , slit=0.7″ (% into slit relative to plot ~ 0.7), airmass=1.0
count rate ~5500A: 1 e-/sec/Å * 0.05 Å /pixel * 10^(0.4*(18.4-15)) * 0.7 = 0.77 e-/pixel/sec
required exp. time: 2500 e-/pixel / 0.77 e-/pixel/sec = 3250 sec.
Readnoise per pixel is small (4-5 DN/pixel), so this simple estimate is approximately correct. Remember that this calculation has to do with the integrated flux over the spatial extent of the source (i.e. peak flux in the spatial direction near 1000 could correspond to a total flux of 2500 DN integrated over all pixels at the same wavelength once you extract the spectrum). Also remember that this calculation assumed 0.8″ seeing and an airmass is near 1. You should adjust accordingly if you have greater slit loses (bad seeing) or are at high airmass.
If you are observing faint objects that are going to give you a relatively small number of counts per pixel in your chosen exposure times, then readnoise will obviously be more important. In this case, you should definitely opt for on-chip binning. As we discuss below, the scale of the CCD detectors is 8.2 pix/” (blue) and 7.5 pix/” (red). So if you are using a slit which is wider than 0.5″, you should bin to minimize amplifier noise. For example:
Flux of target star: V=18 mag
Desired SNR: 20 per pixel (i.e. ~ 400 e-/pixel)
# Angstroms/pixel: 0.1 Å/pixel red side, w/ x2 binning in spectral direction (y)
seeing, slit, airmass: seeing=0.6″, slit=0.7″ (% into slit relative to plot ~ 95%), airmass=1
count rate ~5500A: 1 e-/sec/Å * 0.1 Å /pixel * 10^(0.4*(18.4-18)) * 0.95 = 0.14 e-/pixel/sec
required exp. time: 400 e-/pixel / 0.14 e-/pixel/sec = 46 min.
- Fast 2×2: 28sec (the same for both blue and red)
- Fast 1×1: 87sec (the same for both blue and red)
- Slow 2×2: blue – 41sec / red – 48sec
- Slow 1×1: blue – 134sec / red – 157sec
Data taken with both the red and blue sides should be linear up to the digital saturation of the A/D converters, with the exception of blue-side data taken between May 2004 and Sept 20, 2005 (using Lincoln Labs CCD, installed May 2004).
Until Sept 20, 2005, two linearity problems affected the Lincoln Labs CCD that was installed in May 2004. These problems were measured and reported by Ian Thompson. First, for reasons apparently having to do with the electronics, individual pixels appeared to saturate at about 8,000 DN. For all unbinned observations (1×1 readout), saturation set in around 8,000 DN. Second, the amplifiers appear to saturate at about 16,000 DN. For all binned observations, saturation appeared to set in at around 16,000 DN. As of Sept 2005, Ian reports that both of these problems have been fixed.
A. Internal comparison source:
MIKE has an internal Thorium Argon lamp. The vast majority of the time, and certainly for the standard set-up, this is what you want to use for arcs. It can be turned on and off from the remote control box in the data room. The switch labeled “comparison lamp” will both turn on the lamp and move a flipper mounted mirror into place to direct the light onto the slit. A 1 sec exposure is okay for the blue side and most of the red side. You will notice that there are strong lines which become very saturated in the orders around 7500Å . If you display the images with the right stretch, you’ll see that the saturation isn’t as bad as it looks. These regions do not pose a calibration problem. However, you may also notice that the reddest 10 orders or so have fairly few strong lines. This is a bigger problem. Be sure to look closely at these orders to be sure you’re getting the counts you need. When binned 2×2, a 1 sec exposure is adequate, but a 5 sec exposure gives you more lines. Wavelength and order maps can be found on the main MIKE web site at LCO.
It is very important not to leave the internal ThAr lamp on when it is not needed because it has a lifetime of only a few hundred hours and external sources will not be bright enough for blue-side calibration. The required exposure time is nice and short, so please get into the habit of turning it off promptly when the exposure shutters close. It is not possible to accidentally leave the arc lamp on during an exposure because the arc light floods the slit viewer with light. It’s hard to ignore and it is impossible to place an object on the slit in this state.
B. External comparison source:
It is also possible to use external calibration lamps for the red side, although it is extremely unusual to use these and probably not necessary. If you want to use them for some reason (for above 9500Å?), you need to move the flat field screen into place using the DCU GUI shown below. The GUI is usually already running on the observer’s desktop. If not, it can be found among the applications.
The row of boxes represent individual arc lamps mounted near the screen. The available lamps are Neon, Argon, and Helium. Ar + Ne together work well for the red orders. Click on one of the buttons to turn on the lamp. The button will turn red when the lamp is on. Click it again to turn it off. Below the row of arc lamps is a row of boxes that move the flat field screen in and out of the telescope field of view. When the screen is in, the button next to “FF-Screen” will read “deployed”. A few seconds is adequate for the red side. Use the internal comparison source for the blue side.
C. Internal incandescent Lamp:
There is also an internal flat field lamp which is controlled from the box in the control room. You can turn on this lamp simply by flipping the arc-lamp switch down instead of up. The label of the switch indicates this. This lamp works very well for flats on the red side, with or without the diffuser slide (milky flat slide). It is not very bright on the blue side. Methods for taking flats are discussed further below (Section 7c).
7. Taking data:
A. Selecting a slit:
MIKE has a polished reflecting slit plate with a variety of slits machined into it. Behind the slit plate is a fixed plate which blocks the light from all of the slits except the one which is positioned in front of a single hole at the center of the field. The slit plate is mounted on a motorized stage so that any of the slits can be positioned in front of the single hole in the blocking plate. The telescope operator will know where the blocking plate is located on the slit viewing camera. He will mark on the slit viewer the position where the desired slit should be located for observing and will help you position the slit. The pixel scale on the slit viewing camera is 0.067″ per pixel, so you can see the position of the slit with good resolution.
The easiest way to select a slit during the day is by using the internal flat field lamp to illuminate the slit plate. Because this is an internal lamp, the state of the telescope is irrelevant (i.e. the mirror covers can be closed). The lamp will flood the slit viewing camera with very bright light, and so it will need to be adjusted for large dynamic range (using the “span” command on the slit viewing camera). It is basically not possible to do this without a little experience, so you should ask the Instrument Specialist or Telescope Operator for help selecting the slit you want to use during the afternoon at the start of your run. Once you can see the slits in the slit viewer, just use the switches on the control box to move the slit plate to the right or left and select a slit. The switches are well labeled. There is a handy knob for controlling the speed of the slit motion.
There is no encoder to identify the exact position of the slit plate. We are working on this, however it is relatively easy to move the slit and return it to within 1 pixel in the dispersion direction just by eye in the slit viewing camera (see below). Because standard arcs tell you the wavelength position of the spectra, it is not a problem to move the slit between exposures or use multiple slits during a run. Arcs should be taken every 30-60 minutes, anyway, as discussed below.
This is what you will see in the slit viewer (left) and a schematic drawing of the slit viewer plate (right):
Available slits from left to right on the slit viewer screen are as follows:
Aperture Pairs (separation 3″):
1 0.35 x 0.35 (for focusing)
2 1.00 x 0.35
3 1.00 x 0.50
4 1.00 x 0.70
5 1.00 x 1.00
6 1.50 x 0.35
7 1.50 x 0.50
8 1.50 x 0.70
9 1.50 x 1.00
10 1.50 x 1.50
11 2.00 x 0.35
12 2.00 x 0.50
13 2.00 x 0.70
14 2.00 x 1.00
15 2.00 x 1.50
16 2.00 x 2.00
17 0.35 x 5.00
18 0.50 x 5.00
19 0.70 x 5.00
20 1.00 x 5.00
21 1.50 x 5.00
22 2.00 x 5.00
Most of the available slits are in fact pairs of apertures. You can use these to observe in “A-B” mode, in which you would obtain one exposure with the star in the top aperture followed by a second exposure with the star in the bottom aperture. One aperture is then “object” and one is “sky” in the “A” exposure, and swapped in the “B” exposure. An easily-identified spatial portion of the slit is dedicated to sky and the object this way. This lets you bin the data very aggressively in the cross dispersion (x) direction; you can bin by 4 with the 2 arcsecond apertures. Binning is limited by the 1″ gap between the slits. Because the 1.5″-long aperture pairs are 1.5″ apart, you can bin be larger values with these apertures. A-B mode is especially useful when observing very faint objects because it is possible to locate and sky subtract very faint objects this way. On the other hand, MIKE does not currently have an atmospheric dispersion corrector. (We are in the process of adding one.) So if you are observing at airmasses higher than 1.2, you will have some light at blue wavelengths dispersed out of the short apertures. Also, if you are working an a crowded field, it may not be possible to use the paired apertures and always get a clean measurement of sky.
B. Wavelength Calibration:
The internal ThAr lamp described above (see “Lamps”) can be used to take all the arcs you should need during your run. We often bin by 2 in y (spectral direction) on both sides, and find that a 1 sec exposure gives adequate flux (even at >7600Å ) to obtain wavelength solutions with residuals <0.04 pix rms with a standard IRAF reduction. However, we find 5 sec arcs give us more lines to work with at the red end. We therefore recommend about a 5-10 sec exposure time for the internal ThAr arcs depending on your binning. An arc line map is available on the MIKE web site at LCO.
C. Flat fields:
Because this is an echelle, different colors of light are imaged on the slit in different areas. You want a flat that changes color with position. You wouldn’t want to take a flat without the slit in place. But you do want to fill the CCD with light (even between orders!) in order to get a good flat field image for pixel-to-pixel sensitivity corrections. To do this, a diffusing glass slide can be positioned in the optical path just downstream of the slit for taking “milky flats.” This “milky flat” slide will blur the slit image into a roughly 40-50 pixel smudge. A 40-50 pixel smudge is a good size because it means that there is not much light shared between orders in the flat, but the gaps are well illuminated. This lets you flat field at the edges of the orders.
The diffusing slide is mounted on a sliding post and can be positioned in or out of the optical beam manually. The post sticks through the blue adapter plate below and left of the blue dewar (between the blue and red dewars) and has a brass knob on the end. When the knob is pushed in (flush with the adapter plate), the diffuser is out of the beam. When the slide is pulled out, the diffuser is in position for milky flats. There is a detent at each position. Push and pull firmly and slowly. The brass knob is well labeled.
To take good flats, you need a light source which supplies a lot of photons and does not have strong spectral features. The internal incandescent lamp is fine on the red side of MIKE, but it does not supply much light for the blue side. For that reason, we STRONGLY suggest that you take some milky flats during twilight using an O or B star. We have found that a star with V=4-5 mag gives very good flats in about 25 sec per exposure. It is a good idea to take half of the flats with the star at one end of the slit, and half with the star at the other end of the slit. That way, the inter-order region is better illuminated than if you only position the star in the center of the slit. The best stars for this purpose are stars with high rotational velocities – high v*sin(i). We have left a catalog of such stars with the Telescope Operators (“high_vsini_obscat.cat”). The stars on this list have high enough Doppler shifts that all spectral features are very broad and can easily be median smoothed out with a 1×31 kernel to produce a very nice flat field image. It is relatively easy to take 10 exposures in twilight per night. They can be combined over a run if you have multiple nights. We have found the flats to be pretty stable.
D. Atmospheric Dispersion
MIKE was designed to be mounted at the Nasmyth or auxiliary port. We expect that the preferred observing strategy will be to use MIKE in a gravity invariant mode in which it is mounted on the East Nasmyth platform and does not rotate with the instrument rotator. This is the only mode available now. The virtue of this mode is obviously the stability of the instrument. The down side is that the slit orientation on the sky cannot be changed. The only potential difficulty this poses for point sources has to do with atmospheric dispersion away from zenith. For that reason, we have positioned MIKE at a 30 angle to the platform. At this angle, atmospheric dispersion lies exactly along the slit when observing at a zenith angle of 30 deg.
The figure below shows the atmospheric dispersion (3500-9000Å) across and along the slit as a function of zenith angle for MIKE in its standard position (tilted by 30 deg) on the Nasmyth platform. At a zenith angle of 30 deg, the dispersion is entirely along the slit with a magnitude of about 1.1″. The dispersion across the slit is small (<0.3″) for all zenith angles less than 40 deg. At higher zenith angles (>50 deg), atmospheric dispersion across the slit is significant. With the 5″–long slits, most of the light should get into the slit at zenith angles less than 60 deg. If you are using one of the aperture pairs (2″–long slits or shorter) and are interested in the full wavelength range, then it is probably better to avoid zenith angles greater than about 40 deg.
E. Recommendations regarding calibration:
Bias: Occasional jumps in the bias level occur but can be subtracted out nicely by using an average of the overscan region at the end of each row (x=2048:2176,y=*, unbinned). The highly repeatable bias ramp which occurs at the beginning of each row can be easily subtracted using the overscan at the end of each column (x=*, y=4096:4224, unbinned). Using these overscan regions is more effective than using a combined bias frame. For that reason, 0 sec exposures (bias frames) are not very useful and are not recommended.
Dark: The new Lincoln Labs blue CCD (installed May 2004) has some dark current (~5 DN/hr, depending on running temperature) which will add noise to the exposure but does not appear to have significant 2-D structure over the CCD. Check the dark level during your run and keep this in mind when estimating the signal to noise ratio of your final exposure.
Arcs: It is a good idea to take arcs between long exposures (every 15-60 minutes). Although there is no motion in the 2-D spectrum due to flexure (the instrument doesn’t move), there is motion due to temperature changes of the air, glass, and metal. Over the course of a night, temperature changes can cause small (~ 1pixel) shifts, mostly in the cross-dispersion direction. So the telescope pointing doesn’t affect the wavelength calibration, but time does! It is fine to move the telescope while the data is reading out. It is also fine to take an arc while moving between objects.
Flats: It is a very good idea to take flats with the diffuser for standard pixel-to-pixel flat fielding calibration. You also want to take some flats (either internal lamp or sky flats 0-15 min before sunset) without the diffuser. These can be used for an illumination correction and to trace the edges of the orders. Take an arc at the same time to provide an easy way of identifying the offset between the order position in the flat and the order position in each program exposure. (The orders can move by fractions of a pixel in both the dispersion direction and the cross-dispersion direction due to temperature changes in the spectrograph.)
8. Summary of moving parts:
A. Electronically controlled
A control box is mounted on the side of MIKE for “local” control. A second, remote box is located in the telescope control room. All of the controls are manual switches or knobs and are labeled. Be sure that the local control box switches are set to “REMOTE” so that the slit, comparison, and focus can be controlled from the data room.
1. Slit plate:
The position of the slit is controlled by a motorized stage and positioned using the internal slit-viewing camera as described above (see Taking Data). You can move the slit plate at will to select the slit you want during the night.
2. Internal lamps (Th+Ar lamp and Incandescent lamp)
The lamp switch also controls the flipper mirror as described above (see Comparison Lamps) . You will need to take arcs throughout your observations at night and use the Incandescent lamp for flats during the day.
3. Camera Focus:
The Instrument Specialist will focus MIKE before your run. You should not need to adjust the focus of the spectrograph during your run. So this is for your information only.
Each camera is mounted on an optical bench inside MIKE. The position of each camera relative to the CCD is
controlled by a motor-driven cam which moves the whole bench relative to the CCD. These drives are controlled
remotely from the box in the control room to focus the cameras. The blue camera focuses at a setting of 1.150.
The red camera focuses around 1.050. The optical benches also each contain an invar plate which will move the camera as the aluminum expands or contracts with temperature. This passive thermal control keeps MIKE in good focus over temperature changes as large as 5-10 degrees without any adjustments to the motorized cams. Empirically, the focus is extremely stable. In fact, the best-focus settings do not change appreciably even on 1 year time scales (winter to summer). If you try to refocus the instrument on any given day, you may find a slight change from the previous day if the temperature has changed by more than 5 degrees. However, you are probably just chasing temporary thermal mis-matches in the metal and glass from day to night. These are probably changing fairly consistently between when you focus (afternoon) and when you observe (night). It is not recommended that you try to refocus MIKE for temperature changes smaller than 10 degrees or if the temperature fluctuating through normal 12 hour time scales. If you do try to refocus, try moving in steps of 0.010.
B. Manually controlled:
1. Diffusing slide for “milky flats”.
You will need to move this slide into and out of the beam as necessary during your run to take milky flats.
2. Grating position
The Instrument Specialist will set the grating positions. We do not recommend doing this yourself. If you want a different wavelength range, please specify this in your instrument set-up form. This section is for your information only.
The gratings are positioned manually against preloaded, threaded rods. Dial gauges underneath the red and blue boxes indicate the linear position of the rods, and therefore the position of the grating. There should be no need to move the blue grating. The azimuthal position of the red grating can be adjusted to select the orders which fall on the chip. Each of the gauges and threaded rods are labeled on the spectrograph.
As of May 2004, the standard grating settings and corresponding wavelength coverage are as follows:
Blue Azimuth: 0.346 (was 0.374) Red Azimuth: 0.474 (was 0.535)
Blue Elevation: 0.540 (same) Red Elevation: 0.380 (same)
Orders 71-106 Orders 37 – 70
5000 – 3350 Å 9300-4900 Å
These elevation settings center the free spectral range well, and should not be changed. The azimuthal settings can be adjusted to change the order coverage.
The images beloware of twilight sky about 10 minutes before sunset. Blue is on the left. Both images have (x,y)= (0,0) at the lower left. Because MIKE uses prisms for cross dispersion, the redder orders are always closer together than the blue. This makes it very easy to get your bearings in general. The MIKE web page at LCO also includes arc maps and images with orders labeled (see link in section 7.B:Wavelength Calibration). The strong solar features are easy to identify, as are the atmospheric bands. (CaII H&K are the huge absorption features in the same order near the center of the blue image. The atmospheric A and B bands are the strongest features on the red side.) On the blue side, the spectra get redder towards x=small (on the left) and y=large (at the top). On the red, spectra get redder towards x=large (on the right) and y= small (on the bottom).
9. MIKE data acquisition GUI
The data control window is shown below. To start the window, type “mike” in an xterm on the data control computer. An instrument configuration window will appear, also shown below. The observer can enter his/her name and then select three camera configurations, blue camera only, red camera only, or both blue and red camera. There is an entry for off-line (simulator) operation of the GUI, this is for testing purposes only. Next the observer should select the number of pixels of overscan at the end of each row and the number of bias lines at the end of a readout that should be appended to a frame (128 in x and y is good). Finally the observer can select the telescope, and again an online or offline operation. If the telescope is online then telescope coordinates and various rotator angles are read from the telescope TCS.
The very top portion of the acquisition window has two pull down menus, the first controls the window status (select Exit GUI to exit the window) the second has an entry for user name and another to select the path to the data. This path can be changed without having to restart the window. (You can set up any directory structure you like under ~/DATA/.) These are followed by a bar graph showing the current data disk capacity, and a display of the current UT.
The top half of the window shows information relevant to BOTH the red and blue side, like telescope coordinates, dome temperatures, airmass, etc. Exposures for simultaneous operation of both cameras with all exposure parameters identical are controlled by the Exptime, Start, Pause, Abort, and Loop buttons in the upper right portion of the top half of the GUI. The temperatures of the CCD’s are given in the top half of the window. The current set points are -125 C, and these numbers will turn red if the temperature rises above the set point by more than 5 C.
Entries of numerical values for image number and exposure time will
cause the background in these windows to turn red, the values are
entered into the program when you hit the return key. Other character
fields (white boxes for comments, settings for camera focus values,
grating angles, slit-size) can be simply edited. Entries for X binning,
Y binning, full or subrastered readout, and speed are controlled with
pop up menus, indicated by the presence of a small circle in the right
side of a menu. Two readout speeds are available, a fast, high-noise
mode (full frame readout 95 sec, Read-noise approximately 4.7 e-), and a
slow, low-noise mode (full frame readout 160
sec, Read-noise approximately 3.7 e-). Note that the read times in all cases will be significantly shorter when a camera readout is binned. When exposures are running, the start buttons turn yellow in the exposing cameras. Start/Pause/Abort buttons are beige when those functions are available.
Cameras can also be operated together using the top half of the window or completely independently with the control buttons in the lower left (blue) and lower right (red) portion of the window. Exposure times can be different, exposures can be started asynchronously, and the number of exposures in a loop can be different. Note also that exposure time can be changed during an exposure! Just move the cursor over the “Exp. Time” box in the top half of the window, type a new number, and hit return. This is the easiest way to abort an exposures. You can abort the readout also, if you like, using the abort button.
There are two message windows at the bottom of the GUI. These give the status of an individual readout, both the elapsed read time and the number of lines read and the total number of lines to be read.
The data taking system is pretty robust at this point. We don’t know of anything you should particularly avoid doing. If you do find a way to break the GUI, please tell the Telescope Operator and make sure to include it in the Observer’s Report.
10. Random (very incomplete) Notes for Instrument Specialists:
1- Make sure that all the necessary changes have been made to the guider and Shack-Hartmann parameters before and after the fibers are used with MIKE. This is normally done by the Telescope Operators, but it can be forgotten between crew shifts.
2 – The control box on the side of the instrument has a knob which controls the brightness of the comparison lamp. Turning the knob clockwise makes the lamp brighter. At any setting, the lamp is already too bright, but the power supply doesn’t regulate properly at the lowest setting. There is a mark on the box at or above which the power supply works properly. Leave the knob set to the mark.
3 – If the control box in the observing room doesn’t seem to be working, make sure that the control switch in the box mounted on the side of MIKE is set to REMOTE.
Last updated by rabernst at UM, May 2005.