1. Graphic material for HSC FAQ – March 23, 2013

2. Five things you should know about the Hubble Source Catalog (HSC) 1. Coverage can be very non-uniform, since a wide range of HST instruments, filters, exposure times are included in the HSC. 2. WFPC2, ACS, and WFC3 sources lists are of variable quality. The WFC3 source (which will be incorporated for Version 1 this summer) are deeper, more uniform, and have fewer artifacts. We are in the progress of redoing the older ACS and WFPC2 catalog using the WFC3 algorithms. 3. The default is to show only objects with more than one detections (i.e., Nimages > 1), to minimize artifacts. You will need to request Nimages > 0 to see all the potential objects in the HSC (e.g., to search for transients). (click for details) 4. The default is to use mag_auto SExtractor values for the magnitudes (in the ABMAG system). You will need to request mag_aper2 if you would like SExtractor aperture magnitudes instead. 5. When you display HSC positions (obtained from a combination of images), they may not line up well on the specific image you are looking at. A facility is being developed to address this problem. (Note: This image also shows the “doubling”, artifact – see FAQ # 11)

3. Using N_images > 1 vs. N_images > 0 The default is to use N_images > 1, to insure the source is real. However, there will be cases when a person needs to use N_images > 0. An example is to search for transient (one time) events. BE CAREFUL ! There will be many more artifacts (e.g., blank sources from cosmic rays). However, using N > 1 also removes some real sources. Blink between this VG and the next to see the effect of changing from N_images > 1 to N_images > 0. FAQ # 11 – Artifacts - Blank Sources

4. Using N_images > 1 vs N_images > 0 The default is to use N_images > 1, to insure the source is real. However, there will be cases when a person needs to use N_images > 0. An example is to search for transient (one time) events. BE CAREFUL ! There will be many more artifacts (e.g., blank sources from cosmic rays). However, using N > 1 also removes some real sources. Blink between this VG and the next to see the effect of changing from N_images > 1 to N_images > 0. FAQ # 11 – Artifacts - Blank Sources

5. The yellow circles show the official UDF catalog; green circles show our Nimages > 1 HSC catalog. There are two reasons the HSC does not go as deep in this particular field. 1. The current HLA ACS source lists are not very aggressive. This will be improved by using the new WFC3 algorithms, which will add about ½ of the objects. 2. The HSC uses single-visit images to make the source list. The UDF catalog uses an image where the data for over a hundred visits have been combined. FAQ # 11 – Limitations: The HSC does not go as deep as it is possible to go.

6. A Basic Hubble Source Catalog (HSC) Walkthrough Step 1 - - Enter the HLA (type hla.stsci.edu in your browser window). Click Enter Site here. Click advanced search. Enter 10265 in the Proposal ID: box. Click the Images button. Find the NGC224- DISK color image (3 rd one) and click on Interactive Display. NOTE: If you have not previously used the HLA you may want to check out “Getting started” Step 2 – Click on the Hubble box to see the HSC sources. Pan out and check for uniformity. In the case of the UDF, the uniformity is good, but be aware that it often is not (point to “FIVE THINGS YOU SHOULD KNOW ABOUT THE HSC”. Zoom in and pick star. Click on the star to see the HSC information. Step 3 – Note that the circles are not centered on the stars. Click (FAQ#2) to find out why. The HSC includes data from 27 visits for this star. Scroll over to see magnitudes, etc. For example, the MatchID is 8934299, the mean magnitude in A_F606W = 25.796 and the sigma = 0.032 mag, the position is 00:49:18.777 +42:44:16.82, and the concentration index is CI = 1. 046 +/- 0.036 (i.e., typical of a star) Step 4 – Go to the HSC Summary Search Form (at http://archtest.stsci.edu/hst/hla_cat/ ). Click on Search with Summary Form now Enter the coordinate from above in the Right Ascension and Declination boxes and click Search. We find the same information as we shown on the interactive display. Step 5 - Click on 8923299 to go to the detailed form to see all 27 separate detections (11 in F606W and 16 in F814W) that have been averaged together for the summary form. Note that there is a 28 th nondetection (Det = N) at the bottom for a F435W observations where apparently the star was not bright enough to be included in the HLA source list. Step 6 – Go back to the HSC Summary Search Form to make a catalog to download. Change the radius to 2.0 (arcmin). Change Mag Type MagAper2. Change Output Coordinates to Degrees. Change Output Format to IRAF space-separate w/INDEF. Change Maximum Recods to 10001. Click Search. A catalog with N = 3338 entries will be sent to your computer for you to read (e.g., with texedit or whatever) and save (e.g., using “save as” command in texedit or whatever). Step 7 – Go to the HSC Detailed Summary form. Enter the coordinates. Go to User-specified field 1. Select “Filter” and enter F814W in the Field Description box. This will remove the F606W filter observations which were interleaved in step 5. Move over to Obs. Start Time and click to sort in temporal order. This will make it easier to check for variability (a plotting tool will be added to the HSC for Version 1)http://archtest.stsci.edu/hst/hla_cat/

7. A Basic Hubble Source Catalog (HSC) Walkthrough Step 1 - - Enter the HLA (type hla.stsci.edu in your browser window). Click Enter Site here. Click advanced search. Enter 10265 in the Proposal ID: box. Click the Images button. Find the NGC224- DISK color image (3 rd one) and click on Interactive Display. NOTE: If you have not previously used the HLA you may want to check out “Getting started” Step 2 – Click on the Hubble box to see the HSC sources. Pan out and check for uniformity. In the case of the UDF, the uniformity is good, but be aware that it often is not (point to “FIVE THINGS YOU SHOULD KNOW ABOUT THE HSC”. Zoom in and pick star. Click on the star to see the HSC information. Step 3 – Note that the circles are not centered on the stars. Click (FAQ#2) to find out why. The HSC includes data from 27 visits for this star. Scroll over to see magnitudes, etc. For example, the MatchID is 8934299, the mean magnitude in A_F606W = 25.796 and the sigma = 0.032 mag, the position is 00:49:18.777 +42:44:16.82, and the concentration index is CI = 1. 046 +/- 0.036 (i.e., typical of a star) Step 4 – Go to the HSC Summary Search Form (at http://archtest.stsci.edu/hst/hla_cat/ ). Click on Search with Summary Form now Enter the coordinate from above in the Right Ascension and Declination boxes and click Search. We find the same information as we shown on the interactive display. Step 5 - Click on 8923299 to go to the detailed form to see all 27 separate detections (11 in F606W and 16 in F814W) that have been averaged together for the summary form. Note that there is a 28 th nondetection (Det = N) at the bottom for a F435W observations where apparently the star was not bright enough to be included in the HLA source list. Step 6 – Go back to the HSC Summary Search Form to make a catalog to download. Change the radius to 2.0 (arcmin). Change Mag Type MagAper2. Change Output Coordinates to Degrees. Change Output Format to IRAF space-separate w/INDEF. Change Maximum Recods to 10001. Click Search. A catalog with N = 3338 entries will be sent to your computer for you to read (e.g., with texedit or whatever) and save (e.g., using “save as” command in texedit or whatever). Step 7 – Go to the HSC Detailed Summary form. Enter the coordinates. Go to User-specified field 1. Select “Filter” and enter F814W in the Field Description box. This will remove the F606W filter observations which were interleaved in step 5. Move over to Obs. Start Time and click to sort in temporal order. This will make it easier to check for variability (a plotting tool will be added to the HSC for Version 1)http://archtest.stsci.edu/hst/hla_cat/