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Observing Programs at Keck Observatory with ESI on February 04, 2013 for Prochaska + Associates

This page organizes all of the projects for ESI on February 04. Each program page should include: (i) the optimal setup for the observation; (ii) a target list with finder charts and recommended exposure times; (iii) any additional notes of interest (S/N desired, priority of targets); (iv) Worst conditions (seeing, clouds) under which observations will still be useful.


This project aims to measure hydrogen and metal line column densities in DLA host galaxies and the material in their surroundings. Starting with the QPQ quasar sample, we have identified pairs with a DLA in one sightline. We then use the other QSO in the pair to probe the CGM of the DLA-host galaxy. We would like to use measurements of the hydrogen and metal columns to constrain the ionization state, metallicity, and mass of gas in the CGM sightline. We will also compare the CGM metallicities and low-ionization metal-line kinematics to those measured in the corresponding DLA sightline.

To accomplish this, we must obtain S/N >~ 10 per pix at the wavelength of the DLA's Lya line in the CGM sightline. We are also aiming for S/N >~5 per pix for the DLA itself, and S/N ~ 10 per pix for the DLA's metal-line transitions. I have noted which QSO provides the CGM and DLA sightlines in the target table below.

The target NGC 2623 is just for fun -- it is a nearby merging system driving a strong outflow detected in NaI D absorption in low-resolution IFU data. We'd like to obtain higher-resolution coverage of the Na I D doublet (at 5890 Ang) with ESI.

More instructions on the observing procedure and on using the finding charts are given below the target table.

Finally, if the seeing is > 1.1", or if you're observing through clouds, the QSO observations are probably not going to be successful. If we don't come close to our S/N goals, the data is of limited use.

Also, if you lose time around LST 06h40m-08h40m, just skip J0955 and go straight to J1240. It is better to obtain "complete" observations of a single pair than marginal observations of both (and J1240 is brighter).

Here is the current observing plan:

12 degrees twilight begins at 03:44 LST (19:04 HST), and then begins at 14:48 LST (06:07 HST) in the morning.


Please use the 0.75" slit in echelle mode, unless conditions are extremely good (< 0.7" seeing). Please obtain calibrations for both the 0.75" and 0.5" slit at the beginning of the night (just in case).

Timeline (LST)


03h00m - 03h40m: sky flats, 5 x

03h40m - 05h25m: J0239-0106, 2 x 2700 seconds, 900 seconds acquisition

05h25m - 05h36m: standard star G191B2B, 600 seconds, 60 seconds acquisition

05h36m - 06h40m: NGC 2623, 2x750sec (on object), 2x750sec (on sky), 840 seconds acquisition

06h40m - 11h40m: J0955-0123, 6 x 2850 seconds, 900 seconds acquisition

11h40m - 14h40m: J1240+4329, 4 x 2475 seconds, 900 seconds acquisition

14h40m - 14h51m: standard star HZ_44, 600 seconds, 60 seconds acquisition

14h51m: sky flats and other calibrations, if not done yet


RA (2000)

Dec (2000)

PA [deg]

i_q magnitude


Exposure (s)









19.95, 20.42

3.13, 2.30



RA Offset = -80.3, Dec Offset = 43.9


logsheet_page1.jpg logsheet_page2.jpg

NGC 2623




13.1 (B mag)




Observe sky in separate pointing (see chart)






21.34 (CGM), 20.73 (DLA)

2.84, 2.83, z_DLA = 2.727



RA Offset = 24.0, Dec Offset = -23.7






20.81 (CGM), 20.01 (DLA)

3.26, 3.25, z_DLA = 2.979, 3.097



RA Offset = -55.9, Dec Offset = -3.8


Finding Charts for QSO Pair Targets (J0239-0106, J0955-0123, J1240+4329)

In these charts, the two QSOs are indicated with blue (b/g QSO) and red (f/g QSO) arrows, and the offset star is indicated with a red box. The coordinates at the top (in black) are of the offset star, not the QSOs. The offset star coordinates are also listed in the star list and in the target table above (rather than the coordinates of either QSO). alpha_pos gives the position angle of the pair; this information is also in the star list so that the slit gets set at this angle automatically, but please double check. delta theta gives the separation between the QSOs in arcseconds. The black delta RA and delta Dec (with bars over them) give the offset from the star to the midpoint between the QSOs. These offsets are also included in the star list. A positive RA offset moves the telescope East, and a positive Dec offset moves the telescope North.

The offsets printed in blue and red show how to move from the offset star to the b/g and f/g QSO, respectively. This info should not be needed, however.

Observing Procedure and Finding Chart for NGC 2623

Because this target is larger than the slit length (20 arcsec), this observation will require two pointings -- one for the target itself, and one to observe the sky level. The desired location and orientation (PA = 135 deg) of the slit for the "science" observation is shown on the finder chart in red. The area I'm most interested in is indicated with a white cross. Since this is a diffuse target, please use a blind offset from the indicated offset star (blue) to place the science slit. The coordinates of the offset star are given in the star list, and the offsets are noted in red on the chart. Please obtain 2x750 sec exposures at this pointing.

For the observation of the sky, the exact location is not so important, as long as there aren't any objects or diffuse emission from the galaxy on the slit. I give some approximate coordinates for this pointing in the star list, but don't worry about getting to this exact place. Please obtain 2x750 sec exposures here as well.

Main Pages

Esi2014Feb (last edited 2014-02-05 14:44:58 by MarieLau)