color-selection of OB stars

How to get a simple query criterion to select massive stars in SDSS-V?

Approach:

Find a locus in color-color space that contains hot stars (reddened by different amounts);

Then use Gaia parallax information (NOT: good parallaxes) to weed out all stars in this
color-color-locus that are inconsistent with being luminous (absK<0), or too faint to
be SDSS-V observable mH<12.

At the end, we need to see how complete and contaminated such a sample is.

Starting point: 

take a sample of W1mag-luminous stars from GDR2 x ALLWISE (courtesy Alcione Mora)

(all stars absW1 < -2, or so) and look at them in some color-color space. Below, the Y-axis is chosen to be constant under reddening.

There is a distinct 'plume' in the bottom left, which is (conjecture) reddened blue (massive, luminous) stars, while the mass of objects around (4,0.4) is luminous giants, AGB stars etc.. This is verified by comparison with the literature catalog of Galactic OB stars https://heasarc.gsfc.nasa.gov/w3browse/all/galobstars.html (green points).

Possible Implementation:

We must not rely on "good parallaxes" in any query (as they are usually not available); instead we query on sensible initial 2MASS colors, and only existence in the Gaia catalog (G<21), nothing else

SELECT        g.source_id,g.ra,g.dec,g.l,g.b,g.parallax,g.parallax_error,g.pmra,g.pmra_error,g.pmdec,

              g.pmdec_error,g.astrometric_n_good_obs_al,g.astrometric_excess_noise,g.astrometric_chi2_al

              ,g.phot_g_mean_mag,g.phot_bp_mean_mag,g.phot_rp_mean_mag,g.phot_variable_flag,g.teff_val,g.a_g_val,

         tm.j_m,tm.j_msigcom,tm.h_m,tm.h_msigcom,tm.ks_m,tm.ks_msigcom,g.phot_g_mean_mag - tm.h_m AS g_min_h 

FROM gaiadr2.gaia_source AS g

INNER JOIN gaiadr1.tmass_best_neighbour AS xmatch

ON g.source_id = xmatch.source_id

INNER JOIN gaiadr1.tmass_original_valid AS tm

ON tm.tmass_oid = xmatch.tmass_oid

WHERE  b between -15 and 15

and

tm.h_m - tm.ks_m -0.48*(tm.j_m - tm.h_m) between -0.12 and 0.5

and 

tm.j_m - tm.h_m < 0.8

and

tm.h_m < 12.5

This yields (in an analogous color-color) plot a hint of bimodality (with hot stars bottom left plume, again) ...  but these distributions (1.7M stars) are mushy.

We now excise all stars where Gaia information tells us that they are inconsistent (at say 1 sigma) with being luminous, absK< 0, (i.e. OB stars) (After 7Myears, H<0 corresponds to M>5M_sun; Padova isochrones, is that correct?). Effectively this does a ``forground clean".

kmag + 5log10(parallax+parallax_error)-10 < 0. This leaves 0.6M stars (i.e. 1.1M stars excised).

Note again that Gaia only comes in in two ways:

-- there must be some detection (G<21-ish)

-- and Gaia parallax measurement (however 'lousy') must not be inconsistent with this being a luminous star.

This yields a nice hot-stars r-- red giant/AGB bimodality; showing that the color-color locus of reddened hot stars is distinct from that of RGB, RC, AGB etc. stars. This is illustrated again by comparison with literature OB stars (reference above)

Taking the lower part of this bimodal distribution leaves ~75k candidates M>5M_sun and m_H<12.5; they are very much concentrated to the Galactic plane; the stripy pattern is Gaia scanning law....

Data at: https://www.dropbox.com/s/ogxmtxag05slkeg/initial_JHK_color_cut_consistent_with_K%3C0_J-H-W1_color_cut.fits?dl=0

Clearly all this needs verification, clean up etc.. but that's what I mean by algorithmic selection.

A few notes:

-- need to check how good or bad this initial strawman selection is

-- this could be done in a single query

-- we should understand why the bluest stars from the literature are being missed (Rigel too bright etc..)

-- the bimodality-based sample-selection should not be done by hand as here

-- when challenged, I could do the same for low-mass young stars; but I leave this to experts.

Identifying RC stars in Gaia data, and making 3D or 6D maps with them

From YST: can you remind me how do you infer the distance modulus is phot_g_mean_mag+1.27-1.5*bp_rp ? I always thought distance modulus is apparent - absolute magnitude. In other words, why 1.27-1.5*bp_rp is a good approximation for g band absolute magnitude?

Qualitatively, this is based on the fact that RC stars are remarkably good standard candles
in the near IR, say W1. Then you can ask, can I predict the W1 apparent magnitude from
phot_g_mean_mag and bp_rp, combining the effects of effective temperature spread
and reddening: and phot_g_mean_mag -1.5*bp_rp+ const. is the answer.

Then operationally you can take the RCs in APOGEE (which have a range of temperatures
and reddenings, and [Fe/H]..) and ask

what constant (and what bp_rp slope) to I need to predict the parallax (not the distance)
for the whole sample:
varpi_predicted = 10^ (  -(phot_g_mean_mag -a * bp_rp + b  - 10)/5)
and solve for a and b in a chi2 sense (varpi_obs - varpi_predicted)

Then you can go to clusters etc.. and ask whether there are any Teff,[Fe/H] residuals,
which there seem to be none at the 1% level...

Notes on transformation to Galactocentric restframe

What's the best way to transform to Galactocentric restframe?
We have new pieces of information:
8122pc
proper motion of Sgr A*
we are 25pc above plane (Juric)
and we have radial velocity constraints\

Do we want to write/publish a note on this?

Enceladus shells

Just a note: Helmi is interested in locating Enceladus shells, using RR Lyra.
Plan is to make plots in R_GC and look for peaks in p(R_GC) at low v_tan

Reconstructing the center to edge spectra of stars in eclipsing binaries

Anish Amarsi showed (at GC Retreat 2018) that for the Sun, it is highly informative to analyze spectra from different parts of the disk, effectively spectra emerging under different angles from the photosphere; this is "straightfoward" for the Sun, as it is well resolved.

It looks like the math of doing this from multi-epoch spectra of eclipsing binaries is very straightfoward.

A very cursory check of the literature indicates that some efforts have been made in this direction (using H-alpha line profile to make a surface map etc..); but HWR has seen nothing comprehensive
to solve the problem:
Given a set of high-quality spectra of eclipsing binary stars, with sufficient phase coverage and known orbit geometry, is there a straightforward way to reconstruct rigorously the entire spectra of both stars, as a function of distance from the center; presuming cylindrical symmetry.

The answer to this question seems to be "yes, there is a simple way to do this"; see below.
This would afford spectra of the stars as function of the angle in the photosphere under which
these spectra emerge.

But before doing anything about this, HWR (who has chatted with Kareem about this for a minute)
would like to know/understand a few things form the stellar spectra experts (i.e. Anish/Karen):

• Is this actually an established approach, and HWR has just not found the relevant literature?
• How useful would it be to have spectra = f(cos theta) for different (mostly) MS stars, presumably across a wide range of Teff, and a modest range ( - 1.  <[Fe/H]<0.3 ) of metallicities (because bright eclipsing binaries are not that common..)?
• If useful, is it important this for testing models, or mostly for getting more accurate precise abundances? Or is this just a curiosity?
• If it is interesting in some Teff, FeH regime, what regime is the most interesting?

Having said that, here's a stab at the math of doing this "data driven"; in the naive version this seems very interesting.

Gaia DR2 day0 queries cut and paste

# get all stars with good parallaxes and RGC>12 kpc
SELECT top 100000 *
FROM gdr2mock.main
   WHERE
     parallax/parallax_error  > 8.
      AND
      sqrt( power(8.2-(1./parallax)*cos(l/57.29),2) + power((1./parallax)*sin(l/57.29),2.) )> 12.
      AND
     random_index between 1 and 100000



# find the Ophiuchus stream
select *
from gaiadr2.gaia_source
where
l between 1 and 9
and
b between 27 and 34
and
1./(7.2+0.66*(6.5-l)) < parallax + 2*parallax_error
AND
1./(7.2+0.66*(6.5-l)) > parallax - 2*parallax_error

# get all stars with good parallaxes and RGC>12 kpc

SELECT top 100000 *

FROM gdr2mock.main

   WHERE

     parallax/parallax_error  > 8.

      AND

      sqrt( power(8.2-(1./parallax)*cos(l/57.29),2) + power((1./parallax)*sin(l/57.29),2.) )> 12.

      AND

     random_index between 1 and 100000

# find the Ophiuchus stream

select * 

from gaiadr2.gaia_source

where

l between 1 and 9

and

b between 27 and 34

and

1./(7.2+0.66*(6.5-l)) < parallax + 2*parallax_error

AND

1./(7.2+0.66*(6.5-l)) > parallax - 2*parallax_error 

select *

from gaiadr2.vari_rrlyrae left outer join gaiadr2.gaia_source on (gaiadr2.vari_rrlyrae.source_id = gaiadr2.gaia_source.source_id)

select *

from gaiadr2.vari_cepheid left outer join gaiadr2.gaia_source on (gaiadr2.vari_cepheid.source_id = gaiadr2.gaia_source.source_id)

select *

from user_hrix.apogee_the_payne_coords left outer join gaiadr2.gaia_source on (user_hrix.apogee_the_payne_coords.source_id = gaiadr2.gaia_source.source_id)

select *

from gaiadr2.gaia_source 

WHERE 

random_index between 1 and 600000

select *

from gaiadr2.gaia_source 

WHERE 

radial_velocity IS NOT NULL
and 
random_index between 1 and 600000

select ra,dec,l,b,parallax,parallax_error,pmra,pmra_error,pmdec,pmdec_error,phot_g_mean_mag,phot_bp_mean_mag,phot_rp_mean_mag

from gaiadr2.gaia_source 

where parallax > 20. 

select ra,dec,l,b,parallax,parallax_error,pmra,pmra_error,pmdec,pmdec_error,phot_g_mean_mag,phot_bp_mean_mag,phot_rp_mean_mag,radial_velocity,radial_velocity_error,teff_val

from gaiadr2.gaia_source 

where

radial_velocity IS NOT NULL

select ra,dec,l,b,parallax,parallax_error,pmra,pmra_error,pmdec,pmdec_error,phot_g_mean_mag,phot_bp_mean_mag,phot_rp_mean_mag

from gaiadr2.gaia_source 

where parallax > 10.


# select RC stars around sag
SELECT source_id,ra,dec,parallax,parallax_error,pmra,pmra_error,pmdec,pmdec_error,phot_g_mean_mag,bp_rp,phot_variable_flag,teff_val
FROM gaiadr2.gaia_source
WHERE
(l < 20) or (l>352)
and
b between -45 and 25
AND phot_g_mean_mag + 1.27 -1.5* (bp_rp) between 17.1 and 17.6
and
power( (pmra+2.7)*(pmra+2.7)+(pmdec+1.4)*(pmdec+1.4), 0.5) < 0.7

Last Things I did on the ESA Gaia Aerchive before it went down