White Dwarfs

The white dwarf program in the MWM survey is obtaining multi-epoch BOSS spectra of a large sample of Galactic white dwarfs. These Earth-sized (and consequently intrinsically dim) objects are difficult to identify among the field of much brighter stars. Parallaxes from Gaia have been the key to identifying a homogeneous all sky sample of white dwarfs for spectroscopic follow-up.

Spectra of white dwarfs
Examples of magnetic WD spectra from SDSS observations (Schmidt et al. 2003)

The white dwarf program draws its sample from the Gaia DR2 catalog of white dwarfs (Gentile Fusillo et al. 2019), selecting all targets with a greater than 50% probability of being a white dwarf that are brighter than 20th magnitude in the Gaia DR2 G passband.

In DR20, the white dwarf program draws its sample from Gentile Fusillo et al. (2021), selecting all targets with a greater than 50% probability of being a white dwarf that are brighter than 20th magnitude in the Gaia DR3 G passband.

Cartons


mwm_wd_core

The white dwarf program has a single carton with objects observed both with plates in targeting plan 0.1.0 and with the FPS under targeting plan 0.5.0. The following simple selection function uses Gaia DR2 photometry and the probability of being a white dwarf (PWD) from the catalog of Gentile Fusillo. That catalog can be queried on CasJobs and has been included in the SAS as mos_gaia_dr2_wd.fits.

  • G < 20
  • PWD > 0.5

mwm_wd_gaia_boss

This carton selects White Dwarfs using Gaia DR3 using the following selection criteria.

Selection Criteria
  • par_log = fn.log10(parallax / 100.)
  • G < 20.0
  • parallax * 10^(0.2 * (22. – G)) > 3.
  • (G + 5 * par_log – 0.5 – 5.5 * (bp-rp + 0.5) > 0.)
  • ((bp -rp < 0.4) OR ((bp-rp > 0.4)
  • (G + 5 * par_log) > (11 + 2.2 * (bp-rp – 0.5))
  • (G + 5 * par_log – 6.7 – 2.2 * bp-rp) > 0.) OR (bp-rp < -0.6)
  • Gedr3spur_main.fidelity_v2 > 0.9

Associated cartons for nested cadences:

  • mwm_wd_gaia_boss_2x1
  • mwm_wd_gaia_boss_1x3
  • mwm_wd_gaia_boss_1x2

mwm_wd_pwd_boss

This v1 carton selects white dwarfs using the catalog from Gentile Fusillo et al. (2021) using the following selection criteria.

Selection Criteria
  • PWD > 0.5
  • G <= 20

Associated cartons for nested cadences:

  • mwm_wd_pwd_boss_2x1
  • mwm_wd_pwd_boss_1x3
  • mwm_wd_pwd_boss_1x2

Cadences

All white dwarf targets are observed with the BOSS instrument. In plate operations, they could be observed on plates with any cadence except the RM cadence.

During FPS, mwm_wd_core used the dark_2x1 cadence.

For targeting generations v1.0.2, v1.0.3, v1.0.4 both mwm_wd_gaia_boss and mwm_wd_pwd_boss used the dark_2x1 cadence.

In targeting generations v1.0.5 and v1.0.5-boss-only, mwm_wd_gaia_boss and mwm_wd_pwd_boss used a nested strategy, where the main carton used the preferred cadence of dark_2x2 had higher priority. Then three identical cartons with different cadences were used in order of descending priority *_2x1, *1×3, and *1×2. The cadences in order of priority from highest to lowest was dark_2x2, dark_2x1, dark_1x3, and dark_1x2. This nested structure increased the number of unique targets that the White Dwarf program could observe at the cost of having less than ideal cadences.

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