Should Euclid make 2 passes around the sky?

At the moment, Euclid's wide (15k sqdeg) survey will take all of its data on a given patch
of the sky in one pass (few hours), with some field overlap at the edges.

If the overhead penalty is defensible, it may be conceivable to make two passes around
the sky, taking half the exposure time at each, with the passes separated by ~1 year.

One of the things to think about is which aspects of the time-domain science are enabled by this?

Supernovae? Proper motions of very nearby, very red objects? AGN?


Steps (HWR) for June meeting:

take Mark Cropper's draft of alternate survey strategies, and get Bob Scaramella's
documentation on the survey strategy.

Get Jason involved (weak lensing), Bob Nichol (large scale structure),

Goal:  -- provide the scope document
-- lay out which impact needs to be to be considered:

-- what is the impact of the alternate strategies on the
    basic area-S/N- considerations

-- impact on data reduction, data release policy

-- impact on weak-lensing and LSS science

Distant halo giants using PS1 (incl. proper motions)

Can we use PS1 & (who else?) WISE colors to identify distant halo giants,
using PS1 to weed-out proper motions?
We want tip-of-the-RGB stars that are bright enough for good follow-up, i.e. m_r<19.5,
which should also provide good PM constraints.
What are the candidate source densities?

Things to be checked:
   -- to what distance do we reach with such constraints
   -- what IR photometry coverage do we have and how useful are these colors
   -- what PM do we expect?
   -- probably use either galaxy or Besancon models to explore
 

Value-added information in the APOGEE survey to get stellar ages

This issue came up in the context off what Gaia and Apogee synergies could hold, and in particular on the question of whether Apogee should change its targeting strategy or observation sequence to get better age information.
The two avenues I have pursued are:
 -Observations and targeting of stars on the sub giant-branch with Apogee
 -Repeat observations of giants within 2 parsecs, to compliment astrometric binary orbit solutions with two epoch velocities; A good orbit solution would yield a direct dynamical estimate of the giant mass, thereby constraining its age.

Next actions:
HWR should do estimates over holiday break, so as to present initial results at Seattle, Jan 9, 2015.

Define directions a low latitude

Look up APOGEE target selection criteria

get Besancon models for such criteria

estimate dynamical orbit distances and parallax accuracies

Hypervelocity stars in PS1

Reminded by http://arxiv.org/abs/1411.5022
(which is not immediately applicable): we should check
for high-velocity stars towards the bulge....

Possible next steps are as follows:
Devise an LSD quest that finds candidates. Possible selection criteria could be:
-- within 30° off the bulge
-- at a photometric distance consistent with the bulge
-- certain number of epochs with good photometry
A well-measured proper motion that is consistent with three epochs and
implies a velocity above 300 km per second.

Cepheid in PS1

These are some notes on finding Cepheids in the Galactic disk as a tracer of the younger (<0.5Gyr)
using PS1 (following an ad hoc lunch discussion with Zeljko). Is there something new to be done?

from Richard Anderson's (2013) thesis

What is known?  Literature points towards a catalog by Berdnikov et al (2000,
http://adsabs.harvard.edu/abs/2000A%26AS..143..211B) with 500 Cepheids in the Galaxy. [Note: M31 has about 1500-2000 known Cepheids: http://arxiv.org/pdf/1301.6170v1.pdf]
Reading that Berdnikov paper, I could not gleam anything about the "election function" that led to this catalog. The recent thesis by Richard Anderson (Geneva, 2013) has a nice summary.

This is the distribution of the "known" Galactic Cepheids in apparent mean Bmag vs P[days]

They are a thin disk population (z vs R_GC in kpc)

Who knows what selection function led to this distribution in the X - Y (kpc) spatial distribution...
Is that dust?.

For periods of 5 days, their absolute V-band magnitude (presumably de-reddened) should be -3.4.

This means at a distance of 5 kpc, they should be "easy" for PS1 at  <m_g>=18 for 8 mag of visual extinction....

Things to do:  

• look at the light curves of known Cepheids in PS1

from Richard Anderson's thesis

Peter Yoachim has devised a set of (multi-color) template light curves.

• look at the (bizarre) Wesenheit reddening-free abs. mags. Questions: e.g. at what phase (phase-averaged?) are those corrective colors calculated.?

       

Anderson (2013) thesis

This dereddened magnitude W leads to a far better PLR.

• see how Cepheids show up in a structure-function plot
• 
  

Input from Laurent Eyer (who is one of the variability Gurus for Gaia), who wrote on that 

topic earlier (in a slightly obscure place): 

Gaia should be able to detect 9000 Cepheids; I see few reasons that Gaia can identify many

Cepheids that PS1 can find; so, the potential for 5000 new Galactic disk Cepheids from PS1 compared to 500 in the "state of the art catalog" now?!? 

Here's the communication with Laurent [this site does not accept pdf's with a permalink]:

MAPs and scale lengths with APOGEE RC *'s

Had conversation with Bovy what the trial and tribulations might be to
do MAP scale lengths using the RC stars from APOGEE:

simplest version:
-- focus on apocenter quadrant (bearable reddening)
-- each star in the RC catalog has a distance and a reddening attached to it.
-- to the extent that RC *'s are standard candles, and enter the sample down
   to the apparent magnitude limit, the selection function/volume issue
   should be analogous to the unreddened case, except for exp(-tau_H)/D^2
-- focus on stars at +-4 degrees ftp, the Galactic plane --> don't care about scale-height.


simplest science question, what is R_exp([Fe/H] | [a/Fe]~0)?
is it flat for the metal poor stars?

3D-HST Notes; May 2014

The 3D HST proposal talked a lot about environment dependence of galaxy properties, but nobody has done anything with it, nor seem they eager to do so. I have started to do a little bit of reading up on the practicalities. There is a whole bunch of papers recently that discuss and compare different environment definitions, e.g. Muldrew et al (2012) and Skibba et al (2012). It looks to me that the mark (by stellar mass, compactness, etc..) correlation function is the most sensible way to go, at least Skibba claims it to be so.

I am now combing the literature for comments (solutions) on two specific issues, relevant for 3D-HST:
-- field size (typically 5-ish MPC transverse)
-- grism redshift accuracy: 750 km/s for emission line galaxies, 1500 km/s for absorption line galaxies (m<23); this us squarely between the photo-z surveys and the spectroscopic surveys.

It seems that the PRIMUS folks, in a -- at first glance very nice paper Skibba et al (2014) -- have gone a long way of working out this regime. They have, however, far larger sample sizes and larger (angular) fields. I still haven't found an explicit treatment of field-edges; perhaps the randomization takes care of it.

Basic method of redshift distortions is worked out in Fisher et al (1994).

Also: I don't understand why still "estimators" are used for correlation functions, marked or not,
used. I would presume that any parameterized model for a correlation function (power-law with r0 and gamma) should make a prediction for p(r_p, π  ), which then brings you to likelihood approaches. Why is that not done?

Post discussion lessons:
-- perhaps the simplest and first thing to try is to ask, whether indeed -- at a given mass -- quiescent galaxies ase more clustered than SF ones. How to do this: look at the quiescence-marked correlation, using the unmarked correlation as the "random" (D. Wake's suggestion).