jhRho
commented
7 years ago OK. Here is my draft of answers for the 10 questions, but I would like to check with SN cosmology group for a couple places I marked as "*" (within 1 or 2 days). Since most of answers are here, I am putting the contents here (instead of white paper). I also think making all these answers in one chapter is better (so one can compare one to the other for the same questions. This will also help to avoid repetition of the questions.
Anyway, here they are:
1) Can you place constraints on the tradeoff between the sky coverage and coadded depth? For example, should we maximize the sky coverage (to ~30,000 sq. deg., as e.g. Pan-STARRS) or the number of detected galaxies (the current baseline with 18,000 sq. deg.)?
For most of SN science, multiple observations with optimal time intervals (which will result in increases of coadded depth) are important. The current survey coverage (18,000 sq. deg.) is better than increasing the sky coverage up to ~30,000 sq., since the latter will decrease the number of sampling of a SN light curve. Note that this does not mean that the absolute large sky coverage is not good for SN study and the large sky coverage can help to study cosmic isotropy as long as the quality of light curves is sufficient for SN classification.
2) Can you place constraints on the trade between uniformity of sampling and frequency of sampling? For example, a rolling cadence can provide enhanced sample rates over part or all of the survey part of the time, at the cost of reduced sample rate the rest of the time (while maintaining the nominal total visit counts).
For Type Ia and other SN science, light-curve sampling needs to be about twice or three times as frequent as for the current baseline cadence. The benefits of this improved sampling may have to outweigh the loss of active sky area temporarily (if one add the data less than for 2 months), but over the survey for a year there is NO loss of sky area (see Section 9.4 for details). In trade of the increasing sampling, we may have less number of SNe compared with the baseline cadence, and SNe discovered with LSST (WFD) will have better sampling light curves.
3) Can you place constraints on the tradeoff between the single-visit depth and the number of visits? Especially in the u band, where longer exposures would minimize the impact of the readout noise.
*The longer exposures in the u band is not particularly important for SN science. The number of visits (with optimized time intervals) is more important than the single-visit depth.
4) Can you place constraints on the Galactic plane coverage (spatial coverage, temporal sampling, visits per band)?
The Galactic plane is not the main interest of SN cosmology and SN science. Main interest area is galatic longitude greater than 30 degree.
5) Can you place constraints on the fractions of observing time allocated to each band?
There is no additional contraint to the baseline cadence. A higher number of filter coverage benefits SN detection, and uniformly distributed coverage of each band benefits SN science.
6) Can you place constraints on the cadence for deep drilling fields?
Observing the DDF every night or every the other night for short time (10-15 min) at least for one band will provide good sampling of SN light-curves.
7) Assuming two visits per night, should they be obtained in the same band or not?
- Different band coverage of two visits per night is preferred which will help SN classification.
8) Would your science benefit from a special cadence prescription during commissioning or early in the survey, such as: acquiring a full 10-yr count of visits for a small area (either in all or in selected bands); a greatly enhanced cadence for a small area.
The deep drilling fields would enable early science results of SNe if LSST data were obtained early.
9) Do you have constraints for sampling of observing conditions (e.g. seeing, dark sky, airmass), possibly as a function of band, etc.?
SN science would greatly benefit with good seeing and low airmass since the resulting images will allow to sepearte SNe from the host galaxies and the ISM structures in the galaxies.
10) Do you have science drivers that would require real-time exposure time optimization to obtain nearly constant single-visit limiting depth?
The two images that are used to generate a difference image require real-time exposure time in order to reduce any other residuals than transients including SNe. Other than that, the constant single-visit limiting depth is not critical for SNe.
StephenRidgway
sethdigel
ivezic
drphilmarshall
Dear WP section 9.5 team (@MichelleLochner, @jhrlsst, @rbiswas4, @sethdigel ):
Shamelessly copying Will Clarkson's idea and post, I'm issuing the section authors in exactly the same way to collect responses to this. Once we have responses from each section, @egawiser and I can collate them into a chapter summary.
To help produce conclusions in a form suitable for tradeoffs to be assessed, the chapter editors have been asked (issue #494 ) to task our writing teams with providing short (~1-2 sentence) answers to a list of 10 questions produced by @ivezic, about the material in our chapter sections.
I think this is probably best done through this GitHub system, by entering text straight into this "issue." Therefore, please make an attempt at the questions below, by editing this issue text. (There should be a little crayon-like icon on the far right of the blue title bar for this issue - that's the "edit" button.)
To make this process easier, Zeljko has provided sample answers to the questions, which you can find in the original issue #494. Below is the original request text from @drphilmarshall, followed by the questions.
Cheers -- Michelle
"@ivezic would like to know how each science case constrains the observing cadence in several specific ways, and has provided a list of ten questions he would like answered for each science case - his list is below. Not all the questions will be relevant to every science case, but every science case must present its conclusions, and this list of questions is a very good framework to base them on! Some of the questions address relatively simple fine tuning of survey parameters, while others offer the possibility of dramatic changes. It is particularly valuable to identify constraints or tradeoffs that hold across a broad swath of science programs, and to understand which options, if any, are neutral to the science - by having every science case answer these questions, we will be better able to do that.
To illustrate the expected detail level of answers, we also provide an example for each question (which attempted to reflect real constraints, but are not binding in any way)."
1) Can you place constraints on the tradeoff between the sky coverage and coadded depth? For example, should we maximize the sky coverage (to ~30,000 sq. deg., as e.g. Pan-STARRS) or the number of detected galaxies (the current baseline with 18,000 sq. deg.)?
Our answer comes here:
2) Can you place constraints on the trade between uniformity of sampling and frequency of sampling? For example, a rolling cadence can provide enhanced sample rates over part or all of the survey part of the time, at the cost of reduced sample rate the rest of the time (while maintaining the nominal total visit counts).
Our answer:
3) Can you place constraints on the tradeoff between the single-visit depth and the number of visits? Especially in the u band, where longer exposures would minimize the impact of the readout noise.
Our answer:
4) Can you place constraints on the Galactic plane coverage (spatial coverage, temporal sampling, visits per band)?
Our answer:
5) Can you place constraints on the fractions of observing time allocated to each band?
Our answer:
6) Can you place constraints on the cadence for deep drilling fields?
Our answer:
7) Assuming two visits per night, should they be obtained in the same band or not?
Our answer:
8) Would your science benefit from a special cadence prescription during commissioning or early in the survey, such as: acquiring a full 10-yr count of visits for a small area (either in all or in selected bands); a greatly enhanced cadence for a small area?
Our answer:
9) Do you have constraints for sampling of observing conditions (e.g. seeing, dark sky, airmass), possibly as a function of band, etc.?
Our answer:
10) Do you have science drivers that would require real-time exposure time optimization to obtain nearly constant single-visit limiting depth?
Our answer:
Finally, if your science would benefit from a cadence methodology not covered by these questions, please enter a description of this methodology at http://ls.st/yqq