Super evening: wind at 0Km/h, 50% humidity. Things looked promising for another night of measurements. Right after dusk, we took four 20-minute spectra of WR 140. We then closed the dome to make a few flatfield calibration frames, for the grating position used on the spectrograph. We had not done these calibration frames during the day, because we went shopping, as you can read on the previous post!
Humidity sneaked by while the dome was still closed, and we could not open it again for to measure more targets! Later, the humidity was replaced by strong wind, and cold temperatures came! Now, it's -4.7º outside ?!? Brrr..
What to do? Measure stuff about the camera's RBI (read the post about Residual Bulk Image), the sensor's undesireable elephant memory!
I will soon show what tests we made on the RBI problem.
Saturday, December 20, 2008
Day #5 (2008/12/19)
Today we woke up early (10:00), in result of last night's bad weather. Still, the observatory premises were once again inside a cloud! We decided to go down to a supermarket, in Chio, for shopping, 60km West and 1800m below.
The supermarket was known to be there waiting for us because of Google Earth! But well, 60km in these roads has to be made in 1 hour! So the trip to the supermarket, the gas station, and back took 2 hours. As a result, we were not in time to reserve the dinner at the cantina (deadline for that is 15:00). Next time, I will take the TF-24 road towards East, back to near La Laguna, where there is a vast Cash & Carry, with all sort of stuff!
We decided to have lunch on the restaurant in front of the detour to the observatory at El Portillo. The day's menu was eatable but not as tasty as it sounded. The canary cuisine seems to combine the expertise in condiments and the pragmatism of frozen meat... (Ok, so we are at 2200m, and the closest retailers are at La Orotava, through the "scenicly" slow TF-21 road; we should understand). But Thomas' steak au champignon was very appealing!
Enough sight-seeing and eating, we had to go back to the observatory for preparatory work!
The supermarket was known to be there waiting for us because of Google Earth! But well, 60km in these roads has to be made in 1 hour! So the trip to the supermarket, the gas station, and back took 2 hours. As a result, we were not in time to reserve the dinner at the cantina (deadline for that is 15:00). Next time, I will take the TF-24 road towards East, back to near La Laguna, where there is a vast Cash & Carry, with all sort of stuff!
We decided to have lunch on the restaurant in front of the detour to the observatory at El Portillo. The day's menu was eatable but not as tasty as it sounded. The canary cuisine seems to combine the expertise in condiments and the pragmatism of frozen meat... (Ok, so we are at 2200m, and the closest retailers are at La Orotava, through the "scenicly" slow TF-21 road; we should understand). But Thomas' steak au champignon was very appealing!
Enough sight-seeing and eating, we had to go back to the observatory for preparatory work!
Friday, December 19, 2008
Night #4 /2008/12/18)
Waking up at 12:00 (again), going for lunch, coming back for plat fields, trying to solve the "Neon problem" (Residual Bulk Image), a few mails, a few phone calls, a few tests...
We finally settler for doing some quick darks and bias frames to try and minimize the problem. But this CCD really likes memorizing Ne lines.. It takes time to forget them!
Meanwhile, we decided to tackle the issue of the not-so-good-looking flatfields we were making. We had an intense gradient, and wavy look on our "flats". Later we were reminded that the sensor's sensitivity is it self wavy in aspect. Since a spectrograph physically distributes wavelength on the sensor, it is natural that that something constant is detected by the sensor as darker or brighter in agreement with its sensitivity. The other gradient we have is still unclear in origin. But since a spectrum is only a band of a handful of pixels wide, it doesn't matter! Images that are reduced to produce spectra don't need to be pretty, as noone usually is interested in seeing them.. It is more important that the flat can correctly correct the data, and for that purpose, it works as expected!
During the night, we made 4 20-minute measurements of WR 140, spent some training time trying to point at WR 1, and then 2 more measurements of HD 14134. But we were unexpectedly and abruptly interrupted by a "100% humidity" smell inside the dome! In 20 minutes, humidity had risen from 45% to 100% outside.. We were forced to close the dome, before outside temperature would reach -2.1ºC (dew point at -1.6ºC). These temperatures explain how our car got covered in a bubbly spray of ice! Quite interesting to the touch, but very uncomfortable to stay outside touching it in the cold wind.
Well, a side-effect of this "unfavorable" weather, is that the cumulative 8 hours we had of sleep in the past two mornings, were finally going to be payed back between our pillows and our warm sheets!
Our elephant-memory sensor was left powered on, making dark and bias exposures, during our night of sleep...
Well, I did dedicate part of my sleep time to write the recent posts that should have been written from two days ago..
We finally settler for doing some quick darks and bias frames to try and minimize the problem. But this CCD really likes memorizing Ne lines.. It takes time to forget them!
Meanwhile, we decided to tackle the issue of the not-so-good-looking flatfields we were making. We had an intense gradient, and wavy look on our "flats". Later we were reminded that the sensor's sensitivity is it self wavy in aspect. Since a spectrograph physically distributes wavelength on the sensor, it is natural that that something constant is detected by the sensor as darker or brighter in agreement with its sensitivity. The other gradient we have is still unclear in origin. But since a spectrum is only a band of a handful of pixels wide, it doesn't matter! Images that are reduced to produce spectra don't need to be pretty, as noone usually is interested in seeing them.. It is more important that the flat can correctly correct the data, and for that purpose, it works as expected!
During the night, we made 4 20-minute measurements of WR 140, spent some training time trying to point at WR 1, and then 2 more measurements of HD 14134. But we were unexpectedly and abruptly interrupted by a "100% humidity" smell inside the dome! In 20 minutes, humidity had risen from 45% to 100% outside.. We were forced to close the dome, before outside temperature would reach -2.1ºC (dew point at -1.6ºC). These temperatures explain how our car got covered in a bubbly spray of ice! Quite interesting to the touch, but very uncomfortable to stay outside touching it in the cold wind.
Well, a side-effect of this "unfavorable" weather, is that the cumulative 8 hours we had of sleep in the past two mornings, were finally going to be payed back between our pillows and our warm sheets!
Our elephant-memory sensor was left powered on, making dark and bias exposures, during our night of sleep...
Well, I did dedicate part of my sleep time to write the recent posts that should have been written from two days ago..
Night #3 (2008/12/17)
The "day" started as we left bed, around 12:00. That means 4 hours of sleep, while the CCD camera was left making dark exposures. We started by taking calibration flatfields for the end of the previous night (for the corresponding spectral range), and then made the same stuff for the begining of the night to come (different spectral range).
Our nights are broken in two parts: WR140 observation, with wavelengths around the bnlue-green area (grating position on 9.3 micron), and the H-alpha region for all other targets (grating position at 10.5 micron).
The night was great! Humidity had given us a break for the second consecutive night!
We pointed to some targets and made some spectra of them, but they were not many. We stumbled across a problem: Some images were superimposed with strange emission lines! We spent a lot of time debugging the problem, from over-taping the spectrograph with opaque anti-lightleak adesive stuff, to carefully putting a black bag around the spectrograph and then wrapping it in a double black bag (those used for storing garbage). We then identified the emission lines as those from the calibration lamp, and took the power plug out, to make sure no photon was comming out of the lamp.
The problem would only be correctly identified at the end of the night: RBI (Residual Bulk Image). To make it short the CCD memorizes strong information from the previous integration it made, and also adds it to the next integration. A problem for which we knew not how to choose among solutions. Thos would only be attempted on the next day/night...
Our nights are broken in two parts: WR140 observation, with wavelengths around the bnlue-green area (grating position on 9.3 micron), and the H-alpha region for all other targets (grating position at 10.5 micron).
The night was great! Humidity had given us a break for the second consecutive night!
We pointed to some targets and made some spectra of them, but they were not many. We stumbled across a problem: Some images were superimposed with strange emission lines! We spent a lot of time debugging the problem, from over-taping the spectrograph with opaque anti-lightleak adesive stuff, to carefully putting a black bag around the spectrograph and then wrapping it in a double black bag (those used for storing garbage). We then identified the emission lines as those from the calibration lamp, and took the power plug out, to make sure no photon was comming out of the lamp.
The problem would only be correctly identified at the end of the night: RBI (Residual Bulk Image). To make it short the CCD memorizes strong information from the previous integration it made, and also adds it to the next integration. A problem for which we knew not how to choose among solutions. Thos would only be attempted on the next day/night...
TASCS
The Astronomer Specialized Cleaning System.Our bathroom has a specialized showering system, where the astronomer stands inside a tiny 60x60 cm2 white tub. Half of it is enclosed by 2 cold fixed walls, the other half is delimited by cold flexible colored cloth. Cloth flexibility allows the transit of the astronomer to the interior of the showering chamber. Water temperature is adjusted via a two-knob interface, and is highly susceptible the the astronomer's dexterity in temperature-combination of water. The left know controls the amount of really HOT water, and the left one adjusts the flow of freezing cold water.
The Zen balance between the rotation of both knobs thus yields a pleasant water temperature. Water too hot, burns; water too warm, creates convection air currents that affect the position on the cold wet flexible cloth surrounding the chamber and reducing its usable volume.
On the other hand, water too cold is not preferable to getting stuck on the wet cloth!
The astronomer's bath is thus a daily challenge for which patience and balance should be mastered.
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