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Semester 2001A
Actual Schedule for 2001A
Useful Light Curves
IR Camera Sensitivities
HST Cycle 10
WFPC2 exposure times
WIYN-SYN exposure times

Semester 2001A SCP Search & Follow-up Plan

The general plan is centered around the two themes of improving the statistical uncertainties on the cosmological parameters while also improving tests for systematics such as evolution and abnormal dust. The target sample can be divided into 3 regimes, primarily based on the instrumentation and difficulty in observing them, but also on what science questions they address:

Sample Redshift Range UBV Shift Instrumentation Science Goal
A 0.35 - 0.65 VRI ground-based optical (and NIR for gray dust), plus HST for precision optical photometry spectral feature tests for evolution & long color baseline test for gray dust
B 0.65 - 0.90 RIZ HST F675W,F814W & F850LP fill-in gap in Hubble diagram
C 0.90 - 1.25 IZJ HST F814W & F850LP; ground NIR test for evolution/dust via deviations for a Hubble law

MOSAIC on the CTIO 4m (0.38 sq. deg.) and the 12kx8k camera on CFHT (0.33 sq. deg.) will be used for searching. The searchs have to be scheduled to mesh with spectroscopic screening, which will take place at Keck and possibly a limited amount at the VLT. Of the SNe which are confirmed as Type Ia, 3 of these in the redshift range 0.8 < z < 1.0 and 2 of these in the redshift range z ~ 1.2 will be sent to HST for photometric follow-up. For the z ~ 1.2 SNe, we want to obtain restframe V-band photometry at peak, which requires NIR observations - these are to be obtained using ISSAC at VLT, NIRI at Gemini, and possibly NIRC at Keck (and Subaru?). For several (TBD) of the 0.5 < z < 0.8 SNe which we should also find, we want to obtain photometric follow-up at VLT, NTT, and WIYN. In order to address evolution/dust questions, we would like to obtain a spectral time series and NIR photometry (this plan requires further definition).

In order to deliver the required number and redshift distribution of SNe the searches need to cover about 1 sq. deg. very deeply so that about 5 SNe Ia with 1 < z < 1.2 are expected and about 6 SNe Ia with 0.8 < z < 1 are expected. These numbers need to be refined, but note that we have to allow for uncertainties in the rates as well as statistical (Poisson) fluctuations. The searches should also cover enough area at a shallower depth so we get several SNe Ia with 0.5 < z < 0.8. The timing of the search and follow-up indicates that the searches will have to reach I=25.2 at the threshold S/N so that a SN Ia at -10 days can be detected. Based on the spurious nature of many of the S/N < 5 sources in our last several z > 1 searches, Greg advocates that threshold S/N > 7 be required (meaning S/N > 9.9 in the refs and the news). The last two effects imply that much deeper exposures than in the past be obtained in the deep fields. Indeed, at these signal levels, a subtraction errors as small as 0.4% of sky can generate an artifical source as bright as the SN!

Exposure time estimates vary. The NOAO CTE calculator claims that for the CTIO 4m with 1.1 arcsecond seeing, airmass 1.3, and 6 days from new moon, required exposure is 3.9 hrs. Based on published zero-points, CFHT12k is 25% better at I-band, so exposures of 3.1 hrs are required there. If the seeing is 0.8 arcseconds, the exposures decrease by a factor of 2, to 2.0 hrs for CTIO and 1.6 hrs for CFHT. However, measurements from the spring 2000 CFHT search indicate that I=25.2 has S/N = 5.3 (after subtraction) in 8640 seconds in 0.8 arcsec seeing. Thus to get to S/N = 7 requires 4.1 hrs on CFHT. This agrees very well with the Keck search for Albinoni, after accounting for the 1.4x brighter sky using that search. Therefore, the recommended exposure times are 5.4 hrs for CTIO and 4.1 hrs for CFHT in I-band to reach I=25.2 with S/N > 7 in the subtracted image for 0.8 arcsec seeing.

No single field is visible all night. For safety all the HST SNe should come from one field (up to 1 degree in radius). z < 0.8 (non-HST) SNe are being followed from the ground. Ground follow-up requires visibility for up to two months after discovery, so there should be a z < 0.8 field visible in the last hours of the night during the reference runs. The HST field must be visible during the all but the last hours of the night between the time of the reference and the last NIR imaging. Note that under this arrangement, the HST field fill be searched in I-band, while the z < 0.8 field can/should be searched in R-band. Thus, up to 1st quarter moon can be tolerated for the references and searches.

There was some discussion regarding the optimal gap between the reference and the search. This needs to be simulated so not too many stale SNe are found and so that spectroscopy is taken just before peak so that HST photometry does not miss peak. Roughly speaking, we need at least 3 days from the end of the search to the start of Keck spectroscopy and HST observations can't begin until 5 days after the end of Keck spectroscopy. If we get 6 nights at Keck and all the time is optimally scheduled, this results in 14 days from the end of the search to the first good HST observations. We could obtain short screening exposures within 8 days of the end of the search. All proposals should stress that we need to be consulted before time is scheduled. We need to be in a position to reassess the optimal schedule once we know what allocations we are getting on the many telescopes for which we are proposing.

Due to some creative math, we have 10 HST orbits which are not absolutely needed for the 5 designated HST SNe Ia. These could be put towards screening candidates, longer exposures to mitigate against CTE, or to obtain final reference images for HST SNe in need. These options do not directly impact the upcoming proposals, but should be borne in mind. (Note, we can specify that the SNe be placed closer to the readout amplifier (at pixel 200,200) to mitigate CTE effects.)

Another strategy question is whether to apply for LRIS, ESI, or both on Keck. ESI is the only dark-time instrument on Keck II, whereas Keck I has to support LRIS and HIRES during dark time. It is possible that the easiest way to schedule our 6 nights would be to propose for time on both telescopes (but not simultaneously!). Here is a link to a table comparing the two spectrographs: LRIS/ESI Summary

Proposals to NOAO should emphasize that we took a break from searching at CTIO and follow-up at WIYN so that we could pursue necessary discovery and observations of low-z SNe. That effort was successful and should allow us to push known systematic uncertainties down enough so that samples of up to 200 SNe will be dominated by statistical uncertainties. Thus, we are continuing our pursuit of more SNe Ia to constain the cosmological parameters. We have also obtained, and will continue with, observations designed to test proposed systematics such as evolution and extinction by abnormal dust.

Proposals should also note that we are going much fainter than the DeepLens survey, and that their fields are not well-placed for Keck and VLT follow-up during the desired search period. Thus, regretably we will be unable to leverage off the DeepLens data for this search.

For reference, here are the DeepLens fields:

            RA  (J2000)  DEC        l,b      E(B-V)
         00:53:25.3  +12:33:55   125, -50    0.06
         09:19:32.4  +30:00:00   197,  44    0.02

         05:20:00    -49:00:00   255, -35    0.02
         10:52:00    -05:00:00   257,  47    0.025
         13:59:20    -11:03:00   328,  49    0.05  <--- this may be usable
         NOAO WDFS fields:
         02:10:00    -04:30:00   166, -61   <0.04
         14:32:06    +34:16:48    57,  63    0.015

Semester 2001A Proposals

Prop# Observatory Telescope Due Date Lead Writers Instrument Nights/Orbits Subject Status
1 Keck I / II 09/15/00 Perlmutter Hook Perlmutter Aldering both LRIS and/or ESI 6 spectroscopic screen/type/z 0.5 < z < 1.2 submitted
2 Keck II 10/06/00 Ellis not assigned? ESI 3? spectroscopic series/back-up not ready
I 10/06/00 Ellis same as above NIRC 2? NIR photometry at peak for z > 0.7 not ready
3 UK Gemini Gemini North 09/30/00 Hook Hook NIRI 12 UK hrs queue NIR photometry at peak for z ~ 1.2 submitted Text Figures
4 ESO UT1 and UT2 09/29/00 noon CET Lidman Lidman ISSAC 3 queue NIR photometry near peak 0.5 < z < 1.2 submitted
Lidman FORS 1 visitor or queue spectroscopy 0.5 < z < 0.8 same as above
NTT Lidman SUSI2 3 imaging in R&I of 0.5 < z < 0.8 same as above
5 CFHT 3.6m 09/21/00 24h UT Pain Pain Astier Perlmutter Aldering CFHT12k 6 I-band ref/search 0.5 < z < 1.2 submitted
6 NOAO CTIO 4.0m 09/30/00 Perlmutter Wood-Vasey Knop Aldering MOSAIC 6 I-band ref/search 0.5 < z < 1.2 submitted
WIYN-SYN 09/30/00 Perlmutter same as above MIMO 4 photometric follow-up 0.4 < z < 0.7 same as above
Gemini North 09/30/00 Perlmutter same + Hook NIRI 23 US hrs queue NIR photometry at peak for z ~ 1.2 same as above
MMT not available
7 Yale WIYN 09/30/00? Schaefer Schaefer MiniMosaic 4 screen/photometric follow-up 0.4 < z < 0.7+ not ready
8 Subaru Subaru 11/27/00 Doi/Perlmutter Doi ????? ? Backup spectroscopy? Imaging? submitted (we think!)

Schedule for 2001A

The final schedule is now available.

Old Planning Schedules for 2001A

Greg has prepared possible search scenarios for spring 2001. A scenario for an Apr/May search and for a Mar/Apr search are now available.

At the top of each schedule is a list of the Pros and Cons of each scenario. For each date, the action or event on that date is given. The major phases of the moon are given, and when there is an issue of whether the moon would interfere, the coordinates of the moon are given. For the searches, aside from the refs and news dates, the age is listed for a z = 0.5 and a z = 1.0 Type Ia with s=1 assuming it explodes on the date of the reference image. SNe with no light in the ref with have roughly this age, and those that explode later will be younger. The last follow-up column is not complete, so suggestions here are welcome.

The main problem with an Apr/May search is that there are no good equatorial or southern fields available at the end of the night which don't have of lots of dust and stars. As noted above, SNe to be followed from the ground (z < 0.8 or so) require fields that are well-placed for almost two months after the search so they need to be in the latter part of the night.

HST Cycle 10 (July 2001 - June 2002) Plan

During Cycle 10, neither NICMOS nor ACS will be available. Therefore, it is difficult for us to address science goals other than those we are working on in Cycle 9 (see above). There is a plan to try some demonstration STIS spectroscopy to measure the Si line ratio for a z ~ 0.5 SNe Ia, and the Ca ratio for a z ~ 1.2 SNe Ia. We should also request longer exposure times to help beat CTE, and make it clear that we will move the SN closer to the readout amplifier (this should be done for Cycle 9 as well). We also need to examine whether F850LP filter observations can be of use (despite the low throughput).

Proposals for Future Searches

Prop# Observatory Telescope Due Date Lead Writers Instrument Nights/Orbits Subject Status
1 STScI HST 09/08/00 Perlmutter Perlmutter Aldering WFPC2 150 photometry 0.5 < z < 1.2 submitted
Nugent STIS 20 spectroscopy of z=0.5 and z=1.2 submitted

Useful Lightcurves

  • Redshift 0.5 VRIJ Light Curves
  • Redshift 0.85 RIJ Light Curves
  • Redshift 1.0 IJ Light Curves
  • Redshift 1.2 IJ Light Curves

  • IR Camera Sensitivities

    Here Greg has assembled information from the web pages of current large telescopes with IR cameras. Listed below are the name of the telescope, instrument, and J-band magnitude reached with a given S/N in a give time. Different webpages quote sensitivities for different seeing values; it is assumed that the seeing values that were used are indicative of typical conditions. Also indicated are whether the an instrument has tip-tilt correction or AO correction; if so, the sensitivities are calculated assuming such corrections (since that is what the webpages do).

    Telescope Instrument Tip-Tilt? AO? 50%EED Exposure S/N J-limit
    Gemini NIRI yes* not yet 0.40 60 min 5 24.0
    Gemini QUIRC+Hopaku yes? yes 0.30 60 min 5 23.9
    VLT ISSAC no no 0.60 70 min 5 24.0
    Keck NICR no no 0.60 70 min 5 24.0
    Subaru IRCS no not yet? 0.50 60 min 5 23.4
    Subaru CISCO+OHS no no 0.40 60 min 5 23.6
    Subaru MOIRCS (2004?) yes no 0.40 60 min 5 ??.?

    WFPC2 Exposure Times

    Here are results from the WFPC2 exposure time calculator for SNe at z = 0.85 and z = 1.20. The peak magnitudes are based on our own observations, and the lightcurve is assumed to be sampled when the SN is 0.5 mag below max prior to max, at max, and then 0.5, 1.0, and 1.5 mag below max after max. Exposures are reported to the nearest integral number of orbits, and the resulting photometry uncertain (% err) is shown for the given exposure time calculator. The number of cosmic-ray splits has been taken to be the greater of 2 or the number of orbits.

    Redshift Epoch I mag F675W exp / % err F814W exp / % err F850LP exp / % err
    0.85 maximum 23.5 1 orbit / 0.022 1 orbit / 0.025 3 orbits / 0.036
    0.5 mag wrt max 24.0 1 orbit / 0.031 1 orbit / 0.034
    1.0 mag wrt max 24.5 1 orbit / 0.044 1 orbit / 0.050
    1.5 mag wrt max 25.0 2 orbits / 0.042 2 orbits / 0.048
    final reference 30.0 2 orbits 2 orbits 2 orbits
    1.20 maximum 24.4 2 orbits / 0.030 5 orbits / 0.059
    0.5 mag wrt max 24.9 2 orbits / 0.044
    1.0 mag wrt max 25.4 3 orbits / 0.052
    1.5 mag wrt max 25.9 4 orbits / 0.070
    final reference 30.0 3 orbits 3 orbits

    Links to Proposals

    Greg Aldering (galdering@lbl.gov)
    last updated September 29, 2000, 08:47 PDT