So, if you look over to the right-hand side of this blog, there are a couple of new links, one pointing to my Twitter stream and the other pointing to my new Facebook profile. If you’re the kind of person who is interested in pursuing that sort of thing, feel free to chase down my ever thinning supply of worthwhile thoughts as they spread out in my increasingly deluded attempt to stay hip by belatedly jumping on long overworked netgen trends. (Yikes that’s a long sentence!)
Friday, November 28, 2008
Wednesday, November 26, 2008
Begging for Photons Part II: Finding the limit
So some poking about on websites has yielded some results... First, getting information out of NASA is definitely a “wheat from the chaff” kinda operation. NASA documentation is a bewildering blizzard of information presented in a format that probably made sense to the instrument designers, but is not end-user friendly. Eventually I managed to random-walk my way to an exposure-time calculator.
And this is where I typically meet my second challenge. The late-time spectra of supernovae are weird. They are dominated by line emission, but the lines are actually quite wide, something like about 1/10th of the spectral width of broad band photometric filters in the NIR. (Roughly 600 Angstroms or so for a line near 1.64 microns for the gear-heads out there). Now for several years I’ve been estimating the strength of the late-time emission lines in SNe Ia by extrapolating Peter Meikle’s absolute IR light curves from 100 days post max to the epoch of observation at around 1 year. For the extrapolation I assume that the late-time light curve fades at a rate consistent with the 77 day half-life of Cobalt-56, which is the dominant energy source in the ejecta. This gives me a rough H-band magnitude for the late-time epoch, and has been OK at predicting the strength of the emission, though I haven’t rigorously tested how accurate this is. (Probably not that accurate, I’d guess, but I don’t really have any other method).
Since this method gives me a broad-band magnitude, I then have to convert this to a line flux. Now flux points for broadband magnitudes are actually tabulated as flux densities (ie flux per unit wavelength rather than the actual integrated flux in the band pass). Thus I first have to convert the flux point to a total integrated band flux. If the flux calculation requires a total line flux, then I’m home and dry, but if it wants a flux density, then I have to divide the integrated flux by the width of the line before trying to go on with the calculation. I’ve run into both situations for different instruments, but for the NICMOS calculator it’s just integrated line flux, which is easier.
Then its a matter of choosing settings, clicking on radio buttons and filling in web-forms and after a bit of tweaking it appears that a 900 second exposure would detect my emission line at a S/N of about 1 for a supernova with a broad-band H-magnitude of about 23. That’s pretty good actually. It means I can probably go about 2-3 magnitudes fainter than my ground-based observations and still have some hope of getting enough of a detection to measure a Doppler shift. Hooray.
Now the next question: are there enough targets to make this an interesting program to run in the spring?
And this is where I typically meet my second challenge. The late-time spectra of supernovae are weird. They are dominated by line emission, but the lines are actually quite wide, something like about 1/10th of the spectral width of broad band photometric filters in the NIR. (Roughly 600 Angstroms or so for a line near 1.64 microns for the gear-heads out there). Now for several years I’ve been estimating the strength of the late-time emission lines in SNe Ia by extrapolating Peter Meikle’s absolute IR light curves from 100 days post max to the epoch of observation at around 1 year. For the extrapolation I assume that the late-time light curve fades at a rate consistent with the 77 day half-life of Cobalt-56, which is the dominant energy source in the ejecta. This gives me a rough H-band magnitude for the late-time epoch, and has been OK at predicting the strength of the emission, though I haven’t rigorously tested how accurate this is. (Probably not that accurate, I’d guess, but I don’t really have any other method).
Since this method gives me a broad-band magnitude, I then have to convert this to a line flux. Now flux points for broadband magnitudes are actually tabulated as flux densities (ie flux per unit wavelength rather than the actual integrated flux in the band pass). Thus I first have to convert the flux point to a total integrated band flux. If the flux calculation requires a total line flux, then I’m home and dry, but if it wants a flux density, then I have to divide the integrated flux by the width of the line before trying to go on with the calculation. I’ve run into both situations for different instruments, but for the NICMOS calculator it’s just integrated line flux, which is easier.
Then its a matter of choosing settings, clicking on radio buttons and filling in web-forms and after a bit of tweaking it appears that a 900 second exposure would detect my emission line at a S/N of about 1 for a supernova with a broad-band H-magnitude of about 23. That’s pretty good actually. It means I can probably go about 2-3 magnitudes fainter than my ground-based observations and still have some hope of getting enough of a detection to measure a Doppler shift. Hooray.
Now the next question: are there enough targets to make this an interesting program to run in the spring?
Begging for Photons
If you’re the type interested in peeking behind the curtains, read on:
In late September, the Hubble Space Telescope freaked out. The computer system responsible for transmitting data to the ground crashed. Thankfully, the telescope didn’t completely stop talking to the ground, but it took quite a while for the systems to come back on line. Now, thanks to NASA’s long held religious belief in redundancy, the telescope is once again taking data and transmitting the information back to hungry astronomers on the ground.
Now this failure happened just as NASA was making final preparations for the final servicing mission to HST. Since it wasn’t clear if they’d have to replace the communications electronics, NASA decided to delay the servicing mission again. (For reference, this servicing mission was originally scheduled to happen in 2003 and got sidelined in the aftermath of the Columbia disaster, so HST has been waiting for this visit for a *long* time!) Currently they’re guessing that the servicing mission will be sometime next spring.
Meanwhile, the last round of HST proposals for “Cycle 17” took place last winter and was explicitly expecting to use the new and refurbished instruments after the servicing mission. But that was assuming that the mission was going to be this last spring. It’s now been delayed at least a further year, and the observing queue for approved programs using the existing instruments is running dry. So they’ve put out an emergency call for proposals to fill in the time until the servicing mission. They are specifically looking for proposals which will either use a lot of time (>100 orbits) or “High risk/high gain” type proposals. So the gold rush is on to collect those photons which are about to “fall off the back of a truck,” and it’s time to dig up semi-crazy ideas for what to do with aging HST instruments.
Now one of the side effects of specializing in infrared observations of supernovae, is that while I’ve been able to come up with good uses for the large ground-based telescopes, it’s been much harder to come up with good HST programs. HST has an infrared instrument, but it’s frankly something of an underwhelming instrument. Its design was locked on the wrong side of the rapid development of infrared instrumentation in the 90s and by the time it was deployed, the detectors were well behind the standard for ground-based instrumentation. The field of view is pathetic, the detectors are tiny and noisy, and the sensitivity is nothing to write home about. It does have the advantage of being above the stupendous IR airglow, but even the image quality isn’t that much better than you can achieve with ground-based instruments and the new generation of laser-guide-star adaptive optics. Plus, my particular specialty has been largely spectroscopic science, and the spectroscopic capabilities of NICMOS are poor indeed. So, to date, I’ve largely dismissed NICMOS as useless, at least to me.
But now I’ve run into a different wall. It turns out that Type Ia supernovae have some very interesting behavior in the infrared at late times (roughly a year after the explosion). In particular, the late-time iron features show both a hollow (flat-topped) emission profile and are kinematically offset from the center of the explosion by several thousand kilometers per second. Unfortunately, observing these properties really pushes the sensitivity limits of the biggest telescopes on the planet. Even for supernovae in the nearest galaxies, I need to obtain spectra of objects which are several magnitudes fainter than the sky. These are observations so difficult it even impresses the guys trying to take spectra of type Ia supernovae halfway across the visible universe.
That’s all well and good, if it was easy it would already have been done, but now we’ve reached a point where it’s difficult to build on our successes. We have observed a small handful of objects using a fair bit of time on Subaru and Gemini. But now what we really need are observations of a couple of dozen objects to start looking at how these effects vary and broaden our results to the context of the general population of Type Ia supernovae. However, being limited to the nearest objects, we are stuck with asking for these observations an object or two at a time, and asking for a night or two of 8m time for each. And the TACs are understandably coming back with “what is one more spectrum going to do for you?.” So we’re trying to investigate other avenues. I’ve got a pilot proposal in with Rob Fesen & students to try and use optical data to get at the same science, which might help.
But while pondering these troubles at the SN meeting last week in Japan, I received the e-mail from SCScI announcing the new HST opportunity. So now the question is, can I use HST to learn something about more SNe Ia? My first crazy thought was to try and use the strange filter set on NICMOS to get “photometric redshifts”, using the flux ratios in neighboring filters to estimate the kinematic offsets of the iron lines. Fortunately, after a long night of sushi and sake (including the famously poisonous Fugu... it was a pretty fantastic meeting banquet), I came to my senses and remembered that NICMOS does have a rudimentary spectroscopic capability. The spectral resolution is pathetically low (about 1000 km/s) but in this case that’s actually a plus because it means I will be concentrating the faint emission into just a few pixels. So now it’s down to quantitative questions: (1) is NICMOS even sensitive enough to do this kind of observation, and (2) will I be able to push the observations out sufficiently far to measure an interesting number of supernovae?
To be continued....
In late September, the Hubble Space Telescope freaked out. The computer system responsible for transmitting data to the ground crashed. Thankfully, the telescope didn’t completely stop talking to the ground, but it took quite a while for the systems to come back on line. Now, thanks to NASA’s long held religious belief in redundancy, the telescope is once again taking data and transmitting the information back to hungry astronomers on the ground.
Now this failure happened just as NASA was making final preparations for the final servicing mission to HST. Since it wasn’t clear if they’d have to replace the communications electronics, NASA decided to delay the servicing mission again. (For reference, this servicing mission was originally scheduled to happen in 2003 and got sidelined in the aftermath of the Columbia disaster, so HST has been waiting for this visit for a *long* time!) Currently they’re guessing that the servicing mission will be sometime next spring.
Meanwhile, the last round of HST proposals for “Cycle 17” took place last winter and was explicitly expecting to use the new and refurbished instruments after the servicing mission. But that was assuming that the mission was going to be this last spring. It’s now been delayed at least a further year, and the observing queue for approved programs using the existing instruments is running dry. So they’ve put out an emergency call for proposals to fill in the time until the servicing mission. They are specifically looking for proposals which will either use a lot of time (>100 orbits) or “High risk/high gain” type proposals. So the gold rush is on to collect those photons which are about to “fall off the back of a truck,” and it’s time to dig up semi-crazy ideas for what to do with aging HST instruments.
Now one of the side effects of specializing in infrared observations of supernovae, is that while I’ve been able to come up with good uses for the large ground-based telescopes, it’s been much harder to come up with good HST programs. HST has an infrared instrument, but it’s frankly something of an underwhelming instrument. Its design was locked on the wrong side of the rapid development of infrared instrumentation in the 90s and by the time it was deployed, the detectors were well behind the standard for ground-based instrumentation. The field of view is pathetic, the detectors are tiny and noisy, and the sensitivity is nothing to write home about. It does have the advantage of being above the stupendous IR airglow, but even the image quality isn’t that much better than you can achieve with ground-based instruments and the new generation of laser-guide-star adaptive optics. Plus, my particular specialty has been largely spectroscopic science, and the spectroscopic capabilities of NICMOS are poor indeed. So, to date, I’ve largely dismissed NICMOS as useless, at least to me.
But now I’ve run into a different wall. It turns out that Type Ia supernovae have some very interesting behavior in the infrared at late times (roughly a year after the explosion). In particular, the late-time iron features show both a hollow (flat-topped) emission profile and are kinematically offset from the center of the explosion by several thousand kilometers per second. Unfortunately, observing these properties really pushes the sensitivity limits of the biggest telescopes on the planet. Even for supernovae in the nearest galaxies, I need to obtain spectra of objects which are several magnitudes fainter than the sky. These are observations so difficult it even impresses the guys trying to take spectra of type Ia supernovae halfway across the visible universe.
That’s all well and good, if it was easy it would already have been done, but now we’ve reached a point where it’s difficult to build on our successes. We have observed a small handful of objects using a fair bit of time on Subaru and Gemini. But now what we really need are observations of a couple of dozen objects to start looking at how these effects vary and broaden our results to the context of the general population of Type Ia supernovae. However, being limited to the nearest objects, we are stuck with asking for these observations an object or two at a time, and asking for a night or two of 8m time for each. And the TACs are understandably coming back with “what is one more spectrum going to do for you?.” So we’re trying to investigate other avenues. I’ve got a pilot proposal in with Rob Fesen & students to try and use optical data to get at the same science, which might help.
But while pondering these troubles at the SN meeting last week in Japan, I received the e-mail from SCScI announcing the new HST opportunity. So now the question is, can I use HST to learn something about more SNe Ia? My first crazy thought was to try and use the strange filter set on NICMOS to get “photometric redshifts”, using the flux ratios in neighboring filters to estimate the kinematic offsets of the iron lines. Fortunately, after a long night of sushi and sake (including the famously poisonous Fugu... it was a pretty fantastic meeting banquet), I came to my senses and remembered that NICMOS does have a rudimentary spectroscopic capability. The spectral resolution is pathetically low (about 1000 km/s) but in this case that’s actually a plus because it means I will be concentrating the faint emission into just a few pixels. So now it’s down to quantitative questions: (1) is NICMOS even sensitive enough to do this kind of observation, and (2) will I be able to push the observations out sufficiently far to measure an interesting number of supernovae?
To be continued....
Tuesday, November 25, 2008
Back in the Hurly Burly
Well, I’m newly back from Japan and in less time than it takes to shake off 14 hours of jet lag I’m back in the thick of being faculty. This time of year is really kind of a mess. The triple-whammy of Veterans day, Thanksgiving and finals really makes the last month of the semester something of a jumbled affair. Add to this the chaos of extra end-of-the-semester things like student thesis proposals, teaching evaluation forms, last-minutes committee meetings, and a bonus HST proposal (or two?) and it begins to look like a tasty soup indeed.
Ah well, with all this going on it’s obviously the ideal time to try and discover new ways to spend non-existent free time on the ‘net right? So, just before leaving for Tokyo, I got tagged by a voice from the past (Hi Keith :) ) who’d hunted me down and, among other things, told me that there’s a whole bunch of people that I used to know lurking on Facebook. And indeed, some quick poking around does seem to bear this out. So it seems that I may be sticking my toes into those waters as well.
Meanwhile I need to grade the last month of cosmology homework, invent next weeks last cosmology homework, invent some test questions for the astro seminar quiz, and other sundry teacher stuff. And perhaps write an HST proposal for the Cycle 16 extension using everyones least favorite infrared detector NICMOS. Oh and Tom Maccarone wrote me an email this morning (well morning my time, not his) asking me if I’d like to join him on an HST proposal based on a conversation we had like 2 years ago in Southampton. Sure... why not. Tom’s on facebook too... It’s a funny old world...
Ah well, with all this going on it’s obviously the ideal time to try and discover new ways to spend non-existent free time on the ‘net right? So, just before leaving for Tokyo, I got tagged by a voice from the past (Hi Keith :) ) who’d hunted me down and, among other things, told me that there’s a whole bunch of people that I used to know lurking on Facebook. And indeed, some quick poking around does seem to bear this out. So it seems that I may be sticking my toes into those waters as well.
Meanwhile I need to grade the last month of cosmology homework, invent next weeks last cosmology homework, invent some test questions for the astro seminar quiz, and other sundry teacher stuff. And perhaps write an HST proposal for the Cycle 16 extension using everyones least favorite infrared detector NICMOS. Oh and Tom Maccarone wrote me an email this morning (well morning my time, not his) asking me if I’d like to join him on an HST proposal based on a conversation we had like 2 years ago in Southampton. Sure... why not. Tom’s on facebook too... It’s a funny old world...
Tuesday, November 18, 2008
Not so live from Kashiwa anymore
So the great live blogging experiment hit a couple of predictable roadblocks this afternoon. First, of course, I had to give my own talk, and then I got distracted by a very interesting talk about the Cygnus Loop, and then another interesting discussion about Super-Chandrasekhar-mass Type Ia supernovae. Tomorrow morning I’m chairing the session, so that’s probably not a good time to be doing other things... Ah well. This is the way of experiments...
Had a lovely dinner with the overseas visitors at Ken’s apartment in Kashiwa with some lively conversation, and also had a nice chat earlier with Sergei Blinnikov. All in all a good day. Indeed, this trip has been a nice reminder that it would be nice to get back to being a scientist. I should try and make that happen somehow.
Had a lovely dinner with the overseas visitors at Ken’s apartment in Kashiwa with some lively conversation, and also had a nice chat earlier with Sergei Blinnikov. All in all a good day. Indeed, this trip has been a nice reminder that it would be nice to get back to being a scientist. I should try and make that happen somehow.
Monday, November 17, 2008
LiveBlogging the IPMU supernova workshop: Mamoru Doi
Distant SN Observations with Subaru
Planning to build a 6.5 m IR/Optical telescope in Atacama.
12 IAU SNe in one image! Doi et al. 2002.
Subaru XMM/Newton Deep Survey. Suprime-Cam BVRi’z’ Plus Xrays and NIR (UKIRT). 540 AGN, 400 SNe, 170 Variables, in 1 sq deg.
Delay time distribution. Totani et al 2008 (astro-ph) t^-0.5=-0.2 ... inconclusive so far.
Coming up... Hyper Suprime: 1.5 deg FOV to chase Dark Energy with weak lensing. 2011?
Sullivan et al 2007. Difference between reddening line and BDR in type Ias?
Some discussion here of low Rv again...
30 micron imaging with a 1 m from the ground?
15 Band imaging with dichroics... That’s a kinda crazy instrument, but sorta cool.
Planning to build a 6.5 m IR/Optical telescope in Atacama.
12 IAU SNe in one image! Doi et al. 2002.
Subaru XMM/Newton Deep Survey. Suprime-Cam BVRi’z’ Plus Xrays and NIR (UKIRT). 540 AGN, 400 SNe, 170 Variables, in 1 sq deg.
Delay time distribution. Totani et al 2008 (astro-ph) t^-0.5=-0.2 ... inconclusive so far.
Coming up... Hyper Suprime: 1.5 deg FOV to chase Dark Energy with weak lensing. 2011?
Sullivan et al 2007. Difference between reddening line and BDR in type Ias?
Some discussion here of low Rv again...
30 micron imaging with a 1 m from the ground?
15 Band imaging with dichroics... That’s a kinda crazy instrument, but sorta cool.
LiveBlogging the IPMU supernova workshop: Giuliano Pignata
Low Luminosity IIP SNe
99br... -13.5 mag?!
Low velocity too. Low Ni mass. Low MS mass...
SN 08bk. Very nice data set. A little bump in the LC just after drop off the plateau. 08bk and 99br very similar to one another.
99br... -13.5 mag?!
Low velocity too. Low Ni mass. Low MS mass...
SN 08bk. Very nice data set. A little bump in the LC just after drop off the plateau. 08bk and 99br very similar to one another.
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