[Last Change: 19 Apr 2019 (rev 4) — Page History]

UV and IR PSF

The Chandra Optics were not calibrated in the IR or UV, but certainly do reflect and focus images from IR and UV sources. The detector assemblies include filters designed to reduce or eliminate the possibility of such photons' accumulation by the detector. Several observations on both ACIS-I and ACIS-S were made to quantify any IR and UV light leakage, with Betlegeuse observed for the former and Vega for the latter.

Observations

The complete list of ACIS RAW mode data for Betelgeuse (as of 2015 Sep) is:

OBSID Target CCD Dither Yoff Xoff SIMODE Date-Obs
02593 Betelgeuse I0 Nominal 4.70 -5.68 TE_00528 2002-01-14 13:04:32
03366 Betelgeuse I1 Nominal -4.00 -3.68 TE_00524 2002-01-14 14:46:20
03367 Betelgeuse I2 Nominal 4.70 2.50 TE_00524 2002-01-14 16:32:40
01856 Betelgeuse I3 Off 0.00 0.00 TE_0013C 2000-09-22 11:08:25
03678 Betelgeuse I3 Nominal 0.00 0.00 TN_005EE 2003-02-06 07:57:42
05048 Betelgeuse I3 Nominal 0.00 0.00 TN_005EE 2004-02-02 08:48:16
05963 Betelgeuse I3 Off -0.33 0.00 TN_006E8 2005-02-02 13:46:12
06447 Betelgeuse I3 Nominal -0.33 0.00 TN_00736 2005-11-23 10:17:58
17374 Betelgeuse I3 Off -0.5 -0.1 TN_00C5A 2014-11-20 04:42:26
01855 Betelgeuse S3 Off 0.00 0.00 TE_0013E 2000-09-22 12:52:55
03679 Betelgeuse S3 Nominal 0.00 0.00 TN_005F0 2003-02-06 06:57:42
05049 Betelgeuse S3 Nominal -0.33 0.00 TN_005F0 2004-02-02 07:51:10
05964 Betelgeuse S3 Off -0.33 0.00 TN_006EA 2005-02-02 14:49:43
06448 Betelgeuse S3 Nominal 0.17 0.00 TN_00738 2005-11-23 11:22:57
17376 Betelgeuse S3 Off -0.6 -0.15 TN_006EA 2014-11-16 08:42:19

The complete list of ACIS RAW mode data for Vega (as of 2015 Sep) is:

OBSID Target CCD Dither Yoff Xoff SIMODE Date-Obs
02586 Vega I3 Nominal 0.00 0.00 TE_0013C 2002-02-19 13:03:35
00036 Vega I3 Off 0.00 0.00 TE_0013C 1999-11-05 09:44:17
03685 Vega I3 Nominal 0.00 0.00 TE_0013C 2003-01-27 07:50:40
05046 Vega I3 Nominal 0.00 0.00 TE_0013C 2004-02-05 06:10:26
05961 Vega I3 Off -0.33 0.00 TN_006E8 2005-02-20 21:55:31
06445 Vega I3 Off -0.33 0.00 TN_006E8 2006-01-14 18:30:04
17373 Vega I3 Off -0.1 -0.5 TN_00C5A 2015-08-19 15:53:03
02587 Vega S3 Nominal 0.00 0.00 TE_0013E 2002-02-24 00:38:27
03686 Vega S3 Nominal 0.00 0.00 TE_0013E 2003-01-27 03:23:16
00037 Vega S3 Off 0.00 0.00 TE_0013E 2000-06-07 04:40:58
05047 Vega S3 Nominal -0.33 0.00 TE_0013E 2004-02-05 05:10:57
05962 Vega S3 Off -0.33 0.00 TN_006EA 2005-02-20 22:48:22
06446 Vega S3 Off 0.17 0.00 TN_006EA 2006-01-14 19:25:55
17375 Vega S3 Off -0.15 -0.6 TN_00C5A 2015-08-19 16:35:29

This list includes data where the dither was not turned off. It may be possible for some adventurous soul to correct the dithered data.

For completeness, four observations were carried out with SI modes corresponding to 6-chip TE mode:

OBSID Target CCD Dither Yoff Xoff SIMODE Date-Obs
00984 Vega I0123S67 Nominal 0.00 0.00 TE_002A4 2001-02-01 07:24:10
00985 Vega I23S5678 Nominal 0.00 0.00 TE_002A2 2001-02-01 08:40:25
02594 Betelgeuse I23S1234 Nominal -1.00 0.00 TE_002A2 2001-12-07 12:33:18
03365 Betelgeuse I0123S23 Nominal 4.50 -4.50 TE_002A4 2001-12-16 00:50:10

Observations without dither

This is a list of those data taken with dither turned off. Click on the image to get a FITS file. See below for how the images were created.

ACIS I3ACIS S3
OBSID Target Yoff Xoff nmed Image
36 Vega 0.00 0.00 11 <noautolink>00036.png</noautolink>
1856 Betelgeuse 0.00 0.00 9 <noautolink>01856.png</noautolink>
5961 Vega -0.33 0.00 11 <noautolink>05961.png</noautolink>
5963 Betelgeuse -0.33 0.00 11 <noautolink>05963.png</noautolink>
6445 Vega -0.33 0.00 13 <noautolink>06445.png</noautolink>
17373 Vega -0.1 -0.5 5 <noautolink>17373.png</noautolink>
17374 Betelgeuse -0.1 -0.5 11 <noautolink>17374.png</noautolink>
OBSID Target Yoff Xoff nmed Image
37 Vega 0.00 0.00 5 <noautolink>00037.png</noautolink>
1855 Betelgeuse 0.00 0.00 5 <noautolink>01855.png</noautolink>
5962 Vega -0.33 0.00 5 <noautolink>05962.png</noautolink>
5964 Betelgeuse -0.33 0.00 5 <noautolink>05964.png</noautolink>
6446 Vega 0.17 0.00 5 <noautolink>06446.png</noautolink>
17375 Vega -0.15 -0.6 5 <noautolink>17375.png</noautolink>
17376 Betelgeuse -0.15 -0.6 7 <noautolink>17376.png</noautolink>

Data Reduction

ACIS RAW images are images as read out from the detector (before event processing is performed) with additional bias columns added (eight per node).

Observations were processed with rawmedadd more , a Perl script using PDL which

  1. bias subtracts each frame using the bias columns
  2. groups the frames
  3. generates a median image from each group
  4. sums the median images.

The median process is used to help remove cosmic ray blooms. The number of frames in each group was adjusted by eye to remove the majority of cosmic ray blooms. There is significant residual (non-source related) structure in the resultant image.

Obsid 00037 included some time at the beginning during target acquisition. The raw images for these 89 frames were excluded from the directory prior to running rawmedadd.

The data were processed with the nmed parameter as specified in the above table.

Analysis

Richard J. Edgar, NOv 03, 2013
Terrance J. Gaetz, Nov 30, 2017

We had a detailed look at the data which are presented here.

Chandra observed both Betelgeuse and Vega in the raw mode, looking for optical transmission of the optical blocking filter for ACIS. Each star was observed on S3 and on I3. Small windows, 150x150 pixels, were used in order to avoid saturating the telemetry. There are 10 observations which were not dithered, greatly simplifying the analysis, (Dither would blur the images.) One round of four observations (two stars by two chips) was done in 1999/2000, another in 2005, and two observations of Vega were done in 2006. A few dithered observations were done between 2000 and 2005.

Additional observations with Chandra were obtained for Betelgeuse in Nov 2014, and for Vega in Aug 2015. The 2014/2015 images are much fainter than the earlier data, prompting a reanalysis of the data and a revision to the planning limits. The previous limits were based on scaling from Vega, with the assumption that the magnitude of Vega is 0, and making use of the ratio of the Betelgeuse to Vega fluxes.

The ADUs were summed in a 3x3 pixel region (corresponding to the size of a 3x3 event detection island for X-ray events), and divided by the exposure times to obtain the rate in ADU/sec/9-pixels.

On S3, the raw mode flux for Betelgeuse in late 2014 was over 200 times fainter than in 2005. On I3, the Betelgeuse raw mode flux was at least 10 times fainter in late 2014 than in 2005. For Vega, the source was not clearly visible on either chip. Because scaling from the Vega data is no longer feasible, the revised estimates estimates are now based on the magnitudes provided by by simbad:

  V I J
Vega 0.03 0.10 -0.01
Betelgeuse 0.42 -2.45 -3.00

For planning purposes, the revised limits were calculated as follows.

[1] For Betelgeuse, SIMBAD provides magnitudes of V=0.42, I=-2.45, J=-3.0.

[2] For Betelgeuse, we have 4.5 ADU/sec/3x3-pixel-island deposited. Multiply 4.5 by 3.2 to account for the nominal TE mode frame time to get 14.4 ADU/sec/3.2 sec. The central pixel can have up to 25% of this signal, resulting in 3.6 ADU each frame. In order to cut this signal to 1 ADU, we need objects 1/3.6 as bright as Betelgeuse. On S3: fainter than -1.0 (both I and J) can be observed without worry.

[3] On I3: conservatively estimate Betelgeuse at 1.8 ADU/sec/3x3-pixel-island. This provides about 1.3 ADU in each 3.2 second frame. To cut the rate to 1 ADU per frame, the object needs to be fainter than -2.0 (both I and J). On I3: fainter than -2.0 (both I and J) can be observed without worry.

For reference, the analysis based on the pre-2014 observations is given below.

 
This page is maintained by the CXC Optics Group
CXC logo

The Chandra X-Ray Center (CXC) is operated for NASA by the Smithsonian Astrophysical Observatory. 60 Garden Street, Cambridge, MA 02138 USA.   Email: cxcweb@head.cfa.harvard.edu Smithsonian Institution, Copyright © 1998-2013. All rights reserved.