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Save the Sky: Adventures in Sky Monitoring. Robert J. Nemiroff. Who am I ?. Most cited science papers: GRBs: time dilation, cosmology, lens searches Microlensing: finite source size effects, AGN BLR probe Favorite science papers :

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who am i
Who am I?
  • Most cited science papers:
    • GRBs: time dilation, cosmology, lens searches
    • Microlensing: finite source size effects, AGN BLR probe
  • Favorite science papers:
    • On the Probability of Detection of a Single Gravitational Lens (1989)
    • Visual Distortions Near a Black Hole and Neutron Star (1993)
    • Toward a Continuous Record of the Sky (1999)
    • Tile or Stare? Cadence and Sky-monitoring Observing Strategies That Maximize the Number of Discovered Transients (2003)
who am i know your visitors
Who am I?(Know your visitors)
  • Web:
    • Black hole movies at:

GR correct! (Could make another IAS talk)

    • Astronomy Picture of the Day at:

NASA’s top-ranked site!

save the sky
Save the Sky
  • What happened in the sky last night?
    • Supernova? Nova? Eta Carina flare?

GRB afterglow? Undocumented flash? Flurry of sporadic meteors?

    • Clouds obscure your remote observing?
    • Cirrus affect data on Jan 22 at KPNO?
    • Are clouds rolling in just now?
    • Is last night’s sky gone forever?
save the sky1
Save the Sky
  • Popular Name:

The Night Sky Live Project

  • Web address:
  • Deploys CONtinuous CAMeras (CONCAMs)
concam objectives
CONCAM: Objectives
  • Primary Science
    • Unprecedented temporal monitoring for GRB OTs, meteors, variable stars, comets, novae, supernovae
  • Support Science
    • Unprecedented ability to act as instantaneous cloud monitors, archival cloud monitors, generate all-sky transparency maps, all-sky emissivity maps
  • Education / Outreach
    • Unprecedented ability to show your class last night’s (real) sky, archival skies, monitor meteor showers in real time, show educational sky movies, run educational modules
save the sky 4 concam locations
Save the Sky: 4 CONCAM locations

Kitt Peak

Mt. Wilson

Mauna Kea

Wise Obs.

concam hardware
CONCAM: Hardware
  • CONCAMs are essentially fisheye lenses attached to CCDs run by a PC computer and connected to the internet. CONCAMs do not move - they are completely passive.
    • Most simply put: light comes in the top, electricity comes in the bottom, and data flow out the bottom.
  • In building CONCAMs, we have three montras:
    • “If it moves, it breaks.”
    • “The lens IS the dome.”
    • “Don’t spend 90% of your time trying to get 10% more images.”
concam data
  • All recent images are available through
  • All data are free and public domain.
  • All FITS and JPG data are archived to DVDs (previously CDs).
  • Each CONCAM node generates about 500Mb of raw image data per night.
  • Higher level data products (e.g. photometry) are now being generated in real time for some CONCAMs.
concam scientific milestones
CONCAM Scientific Milestones
  • First CCD device to image the position of a gamma-ray burst during the time of the gamma-ray burst trigger (#1: GRB 001005)
  • Most complete, global, and uniform coverage of a meteor storm: the 2001 Leonids
  • Most complete light curves for hundreds of bright variable stars starting from May 2000, when the first CONCAM was deployed on Kitt Peak.
  • First devices to give real-time optical ground truth for the whole sky in support of major astronomical telescopes, including Gemini North, Keck, Subaru, IRTF, SpaceWatch, Wise, ING 4-m, Mayall 4-M, SARA, and WIYN.
  • In May 2003, fisheye night sky webcams now image most of the night sky, most of the time. For example, were SN 1987A to go off tomorrow, there would be a good chance that a CONCAM saw it.
tile or stare a sky monitor s classic conundrum
Tile or Stare?A sky monitor’s classic conundrum
  • Sky monitoring increasing
    • Current Projects (see BP webpage: abridged, expanded)
    • CONCAM R. J. Nemiroff
    • KAIT A. Filippenko
    • LINEAR LINEAR team
    • LONEOS T. Bowell
    • LOTIS H. S. Park
    • MEGA A. Crotts
    • NEAT E. Helin
    • RAPTOR W. T. Vestrand
    • ROTSE C. Ackerloff
    • Spacewatch R. S. McMillan
    • STARE T. M. Brown
    • SuperMACHO C. Stubbs
    • TAOS C. Alcock
    • YSTAR Y. I. Byun
tile or stare
Tile or Stare?
  • Likely future sky monitoring projects

include (much abridged):

  • Pan-STARRS N. Kaiser
  • LSST A. Tyson
  • GLAST P. F. Michelson
tile or stare assumptions
Tile or Stare?: Assumptions

Generic case considered here:

  • Transients are discovered and confirmed on a time-contiguous series of exposures
  • Sky is isotropic
  • Effective apparent brightness distribution of transients N(l) is already known
  • Once discovered, transients are handed off to a separate follow-up telescope

“Tile or Stare” & tiling cadence determination important for:

  • microlensing, GRB OTs, supernovae, planet detection, binary star eclipses, stellar flares, blazar flares, QSO flares, Near Earth Objects, comets, meteors & more ...
tile or stare the two key power indices
Tile or Stare?The Two Key Power Indices: ,
  • Variables:
    • N: effective apparent cumulative brightness distribution of transients
    • ldim: apparent luminosity at obs. limit
    • te: exposure time
  • At the observation limit, quantify:
    • N  ldim(low background:   -1)
    • ldim te(high background :   -1/2)
  • N  te
tile or stare a mathematical optimization
Tile or Stare?: A Mathematical Optimization
  • Find N(l) from existing observations (l: apparent brightness)
  • Find l(te) from detector, noise, and backgrounds (te: exposure time)
  • Compute N(te) -- might be conveniently parameterized in terms of power-law indices  & 
  • Estimate total time of campaign: tc (exact value usually not important)
  • Find grand total expected transients during campaign: Ng
  • Write Ng is terms of treturn, the time it takes for a survey to return to a given field (i.e. cadence). Read, down and slew times enter here.
  • Compute dNg/dtreturn, find solutions to dNg/dtreturn=0.
  • Find treturn that best maximizes Ng.
tile or stare decision summary
Tile or Stare? Decision Summary
  • If, during exposure, the rate that transients come over the limiting magnitude horizon is increasing fast enough (  > 1), then stare should be preferred.
  • If, on the other hand, the rate that transients come over the limiting magnitude horizon is not increasing fast enough (  < 1), then tile should be preferred.
  • Usually the best tiling cadence is the duration of the transient, since a faster tiling cadence will waste effort on transients that have been previously discovered, while a slower tiling cadence will miss transients occurring in other fields.
  • If, however, the duration of the transient is comparable to the cumulative read-out and/or slew times during a sky-tiling, then a mathematical maximization as described in the preprint will find the most productive cadence.
tile or stare supermacho
Tile or Stare? SuperMACHO
  • Objective: maximize microlensing transients discovered
  • LMC N(l) has  < 1: tile beats stare for identical fields
    • what cadence?
  • LMC not isotropic: fields with highest N(ldim) preferred
    • N(l) may change with seeing or be better determined with time
    • Therefore, choosing the next field to observe is very complicated -- not unlike a chess game. Optimization might involve real-time Monte-Carlo simulations.
  • Field return rate still attracted toward transient “duration of interest”
    • faster cadence inefficiently re-discovers known microlenses (competes with field richness at ldim)
    • “duration of interest” may be the microlens rise time: ~ two weeks, although microlens rise times have wide variety of durations
tile or stare lsst
Tile or Stare?: LSST
  • Objective (example): maximizing Type IA supernovae discovered
  • Sky essentially isotropic (out of Galactic plane)
  • N(l):  > 1 for I < 24: stare preferred
    • effectively creates a minimum observation time per field
  • N(l):  < 1 for I < 24: tile preferred
    • what cadence?
  • Return time (cadence) optimized at the “duration of interest”
    • faster cadence inefficiently re-discovers known supernovae
    • slower cadence inefficiently misses supernovae in neglected fields
    • “duration of interest” could be rise time of SNe: ~ 15 days (1+z)
  • Different cadences will optimize discovery rates for different transients
    • might have Guest Investigators (GIs) program where GIs change filters and cadence to optimize discovery rate of GI-preferred transients
tile or stare glast
Tile or Stare?: GLAST
  • Objective: maximize blazars (quiescent phase) discovered
  • GLAST’s survey mode constrains it to point away from the Earth, but rock at some cadence between the N&S Celestial Poles.
  • N(l) away from Galactic Plane:  > 1: stare
    • stare = GLAST Deep Field (GDF); should maximize detections
    • stare only possible at NCP, SCP or during pointing mode
    • GDF exposures should end if/when faint blazars saturate ( drops below unity)
  • N(1) in Galactic Plane:  < 1: tile
    • GDF strategy inefficient in Galactic Plane
    • quiescent nature allows co-adding at any time, cadence unimportant
  • , , GDF existence, GDF location are energy dependant.