Jenn's Astronomy Project- Photometry (16.280)

Jenn's 16.280 Project Photometry and Other Analysis
Photometry was done on dark subtracted, flat fielded and scaled images (not combined)

Photometry on clear image:

The first run of photometry was done simply to get the fluxes of the stars which appear in the hubble guide star catalogue. These were found to be:

Star Flux Catalogued Magnitude
(emulssion=IIaD)

GSC 2831-001155 83843.91 14.25

GSC 2835-02370 76819.59 14.63

GSC 2831-01237 154211.8 14.13

this information was then used to get the photometric package's magnitude correction value (zmag). The principal behind the zmag is to correlate the fluxes found in our image to the actual magnitudes in the Hubble Guide Star Catalogue(HGSC). To find the zmag we use the following formula as outlined in the polyphot (our photometry package) help pages

zmag=magnitude(HGSC)+2.5log(flux)-log(exposure time)

We found the zmag of all three catalogued stars and averaged them to find a single zmag to put in the parameter files.

Running the photometry package again with the appropriate zmag set we found the following magnitudes for the stars:

Star Magnitude (filter=clear) Difference from HGCS Magnitude

GSC 2831-001155 14.52 0.27

GSC 2835-02370 14.646 0.016

GSC 2831-01237 13.881 0.249

Faintest Magnitude 19.720 ---

A you can probably see there is a fairly large error (about 0.18 when averaged) associated with the values found from my image using polyphot. The reason for this is most likely the fact that the filter we are using has a different transmission curve, width and central wavelength than the one used to find the HGSC magnitudes. Different stars at different temperatures give off different amounts of light over the visible spectrum and so filter specifications could theoretically change a lot when it comes to photometry. We also need to take into account that stars closer to the very bright stars just off camera in my image have a higher background than the average background value which got subtracted off.

We measured both the brightest and faintest magnitudes detected to find out what the magnitude range is across the image and the limiting magnitude of the telescope at this exposure time. The limiting magnitude is simply equal to the faintest magnitude detected (that being 19.720) and the magnitude range is simply the difference between the brightest and faintest magnitudes. 19.720-13.881=5.839 and so the magnitude range across this image is 5.839 magnitudes.

To find the magnitudes of the galaxies we ran polyphot again with the same zmag making a polygon around the galaxy of interest. Our Results were as follows:

Galaxy Flux Magnitude

UGC01810 387156.1 12.862

UGC01813 88895.7 14.459

Next we comparing these to the catalogued brightnesses for these galaxies in NED (which doesn't give a filter):
Galaxy Magnitude from NED Measured Magnitude

UGC01810 13.42 12.862+/-0.18

UGC01813 15.08 14.459+/-0.18

These compare not too badly, but there isn't much more to say than that not having a filter associated with the values from NED.

If there are any keeners out there wanting to take a look at my IRAF polyphot logfiles they are here: Catalogued Stars, UGC01810, UGC01813 and for finding the faintest star.

Luminosity Profiles:

Note in the luminosity profiles the bottom horizontal line is the baseline (aka. background) and the top horizontal line is approximatly 1 sigma above (as best as I could do with the given scale. Also 3 sigma is the standard value to take, but with the large sigmas in these images taking 3 sigma would give me nothing but the bulge.

Across Major axis of UGC01810
(the larger galaxy)
The diameter here goes from where the faint arm crosses the sigma line (57+/-1) to the same point on the farthest arm (206+/-1) and is 149+/-2 pixels. Note, the error here is simply the error in the measurement, it doesn't take into account the error in the baseline or sigma.
Given that each pixel is 0.9 arcseconds (see the Assessment of Basic Image Page) we find that UGC01810 is 2.24+/-0.03 arcminutes across the major axis.
The diameter give by NED is 2.2 arcminutes.

Across Minor axis of UGC01810
The diameter here goes from where the arm crosses the sigma line (22+/-1) to where the bulge drops off and passes the sigma line (100+/-1). The diameter in pixels is 88+/-2 which translates into 1.32+/-0.03 arc minutes
The diameter give by NED is 1.4 arcminutes.

Across fainter arms of UGC01810
I looked at this, not so much for measurement sake but to see the different levels of brightness in the two arms and whether the area between the arms was at all brighter than the background. It's mid level looks to be higher on average but it is still below the sigma line and so it's hard to tell for sure.

Across Major axis of UGC01813
(the smaller galaxy)
The diameter here goes from 24+/-1 to 88+/-2 and so the length of the diameter in pixels is 64+/-3. This corresponds to .96+/-0.05 arcminutes.
The value given by NED is 1.5 arcminutes

Across the Minor axis of UGC01813
This diameter goes from 26+/-1 to 44+/-1 which gives a width of 18+/-2 pixels. This translates into a diameter of 0.27 arcminutes
NED's value for this diameter is 0.4 arcminutes.

Between the two galaxies
Here I was looking to see if I could distinguish a bridge between the galaxies. It appears there is one though the value for the base line here doesn't appear to be correct. Even though it looks high the bridge still peaks over the sigma line.

Photometry on Blue image:

Using the same zmag we ran polyphot (our photometry package) on the red image. Our Results were as follows:

Star Flux Magnitude (filter=clear)

GSC 2831-001155 4867.604 17.613

GSC 2835-02370 7147.996 17.196

GSC 2831-01237 5640.351 17.453

Faintest Magnitude 104.2298 21.786

We measured both the brightest and faintest magnitudes detected to find out what the magnitude range is across the image and the limiting magnitude of the telescope at this exposure time. The limiting magnitude is simply equal to the faintest magnitude detected (that being 21.786) and the magnitude range is simply the difference between the brightest and faintest magnitudes. 21.786-17.196=4.59 and so the magnitude range across this image is 4.59 magnitudes. The reason that this is smaller than the clear images is most likely due to how noisy the blue image is compared to the clear.

Galaxy Flux Magnitude

UGC01810 23971.87 15.882

UGC01813 1764.692 18.715

Comparing these to the magnitudes in B from the LEDA calatlogue (reference on theBasic Information Page) we find:
Galaxy Magnitude from LEDA Measured Magnitude

UGC01810 13.5 +/-less than .3 15.882

UGC01813 15.2+/-less than 0.3 18.715

These don't compare very well at all. Errors may be the size of the apperture used or the fact that my blue image was so noisy. Other factors include the fact that I have yet put much time into finding out the specifications for the emulsion used to find the magnitudes of the HGSC values. If the emulsion is more responsive to the blue then we would find a different zmag based on the blue stars and so the magnitudes of the stars which are currently about 17th magnitude would be 14th and so the values for the galaxies would also be brighter.

If there are any keeners out there wanting to take a look at my IRAF polyphot logfiles they are here: Catalogued Stars, UGC01810, UGC01813 and for finding the faintest star.

Lumionsity Profiles:

note in the luminosity profiles the bottom horizontal line is the baseline (aka. background) and the top horizontal line is approximatly 1 sigma above (as best as I could do with the given scale).

Across Major axis of UGC01810
(the larger galaxy)
The diameter here goes from where the faint arm crosses the sigma line (42+/-2) to the same point on the farthest arm (169+/-1.5) and is 127+/-2.5 pixels. Note, the error here is simply the error in the measurement, it doesn't take into account the error in the baseline or sigma.
Given that each pixel is 0.9 arcseconds (see the Assessment of Basic Image Page) we find that UGC01810 is 1.91+/-0.04 arcminutes across the major axis.
The diameter from the POSS Blue print is 2.1 arcminutes.

Across Minor axis of UGC01810
The diameter here goes from where the arm crosses the sigma line (22=/-1) to where the bulge drops off and passes the sigma line (112+/-1). The diameter in pixels is 90+/-2 which translates into 1.35+/-0.03 arcminutes The diameter from the POSS Blue print is 1.4 arcminutes.

Across Major axis of UGC01813
(the smaller galaxy)
Here it was hard to determine which crossing of the sigma line to use and so I did two, 49+/-1 to 103+/-1 and 109+/-1 which gives respectivly 54+/-2 pixels and 60+/-2 pixels as a diameter which translates into .81 or .9 arcminutes.
The diameter from the POSS blue print is 1.4 arcminutes.

Across the Minor axis of UGC01813
This diameter goes from 26+/-1 to 41+/-1 and gives a diameter of 15+/-1 pixels or .225 arcmin
The POSS blue print diameter is 0.4 arcminutes

Between the two galaxies
This I've chosen to show even though it really doesn't show much at all; that's just the point, if it doesn't exist here the bridge can't consist of young stars.

Photometry on Red image:

Using the same zmag we ran polyphot (our photometry package) on the red image. Our Results were as follows:

Star Flux Magnitude (filter=clear)

GSC 2831-001155 37425.16 15.399

GSC 2835-02370 33151.14 15.530

GSC 2831-01237 67686.27 14.755

Faintest Magnitude 544.7994 19.991

We measured both the brightest and faintest magnitudes detected to find out what the magnitude range is across the image and the limiting magnitude of the telescope at this exposure time. The limiting magnitude is simply equal to the faintest magnitude detected (that being 19.991) and the magnitude range is simply the difference between the brightest and faintest magnitudes. 19.991-14.775=5.216 and so the magnitude range across this image is 5.216 magnitudes which is between the ranges for the clear and blue images which makes sense as the noise in this image was also between that to the clear image and the blue one.

Galaxy Flux Magnitude

UGC01810 124080.6 14.097

UGC01813 34975.27 15.472

Compared to red magnitudes taken by:
Reshetnickov, V.P., Hagen-Thorn, V.A., Yakovleva, V.A,
(Astronomy and Astrophysics, Suppl. 99, 257-289,1992)

Galaxy Magnitude from
above mentioned source Measured Magnitude

UGC01810 12.5+/-2.5 14.097

UGC01813 13.6+/-2.5 15.472

Again the measured values need to be higher to compare with professionally measured values. Again I would need to do more research on the emulsion used for the HGSC values.

If there are any keeners out there wanting to take a look at my IRAF polyphot logfiles they are here: Catalogued Stars, UGC01810, UGC01813 and for finding the faintest star.

Lumionsity Profiles:

The baseline for this image was hard to pin down as there was a definite slope in the background across the image. (see the Assessment of the Basic Image page). What I did in this case was to draw the base line through the center of the noise. Although the noise level changed across the chip, the standard deviation remained fairly consistant. I determined from this that the best sigma line would be parallel to the baseline.

Across Major axis of UGC01810
(the larger galaxy)
The diameter here goes from where the faint arm crosses the sigma line (34+/-1) to the same point on the farthest arm (167+/-1) and is 133+/-2 pixels. Note, the error here is simply the error in the measurement, it doesn't take into account the error in the baseline or sigma.
Given that each pixel is 0.9 arcseconds (see the Assessment of Basic Image Page) we find that UGC01810 is 2.00+/-0.03 arcminutes across the major axis.
The diameter from the POSS Red Print is 1.9 arcminutes.

Across Minor axis of UGC01810 The diameter here goes from where the arm crosses the sigma line (31+/-1) to where the bulge drops off and passes the sigma line (102+/-1). The diameter in pixels is 71+/-2 which translates into 1.07 arcminutes
The diameter from the POSS Red print is 1.3 arcminutes.

Across Major axis of UGC01813
(the smaller galaxy)
It was hard to determine which crossing of the sigma line to use and so I took two for each side. I will calculate the largest and smallest diameters. The diameter here goes from 27+/-1 to 94+/-1 or from 33+/-1 to 91+/-1. This gives a small diameter of 58+/-2 pixels and a large diameter of 67 pixels. These correspond to .87 arcminutes and 1.00 arcminutes respectivly.
The diameter measured from the POSS Red print is 1.4 arcminutes

Across the Minor axis of UGC01813
The diameter here goes from 13+/-1 to 34+/-1 and gives a diameter of 21+/-2 pixels. This corresponds to a diameter of .315 arcminutes. The diameter measured from the POSS Red Print is 0.4 arcminutes.

Between the two galaxies
We do see the bridge in this profile and so we can conclude that the bridge is made of older stars as opposed to younger stars.

Relative Photometry:

The relative photometry that will be done here will be to try and determine which galaxy has more light passing through a specific filter. In principal this can be done by taking the ratio of the magnitudes or fluxes of the galaxy through the clear and coloured filters. The magnitudes don't exactly correspond to the catalogued values and so I felt that the ratio of fluxes would be a better measurement.

What percentage of the light in the clear image is Blue?

For UGC01810 the flux from the blue image over the flux from the clear is:
0.061918

For UGC01813 that same ratio gives:
0.019844

What percentage of the light in the clear image is Red?

For UGC01810 the flux from the red image over the flux from the clear is:0.320492

For UGC01813 that same ratio gives:
0.393442

Having read that there was a starburst which was apparently happening in the smaller companion, UGC01813, I would have expected it to be more blue overall. One thing I hadn't taken into account when making that prediction was that the larger comapanion UGC01810 is practically face on whereas UGC01813 is seen edge on. What is probably happening here is that when the light is travelling out of UGC01813 it is travelling through a lot of dust on it's way. Dust has a tendancy to absorbe blue light and let the red light pass and so the more dust, the reader the light emitted from the galaxy appears.

To try and determine whether or not there is a starburst happening in this galaxy we would have to use other information such as spectra or the total luminosity from interstellar dust as well as the luminosity from the far infrared red. starburst paper on the history page)

<-Back

Star	Flux	Catalogued Magnitude (emulssion=IIaD)
GSC 2831-001155	83843.91	14.25
GSC 2835-02370	76819.59	14.63
GSC 2831-01237	154211.8	14.13

Star	Magnitude (filter=clear)	Difference from HGCS Magnitude
GSC 2831-001155	14.52	0.27
GSC 2835-02370	14.646	0.016
GSC 2831-01237	13.881	0.249
Faintest Magnitude	19.720	---

Galaxy	Flux	Magnitude
UGC01810	387156.1	12.862
UGC01813	88895.7	14.459

Galaxy	Magnitude from NED	Measured Magnitude
UGC01810	13.42	12.862+/-0.18
UGC01813	15.08	14.459+/-0.18

Across Major axis of UGC01810 (the larger galaxy) The diameter here goes from where the faint arm crosses the sigma line (57+/-1) to the same point on the farthest arm (206+/-1) and is 149+/-2 pixels. Note, the error here is simply the error in the measurement, it doesn't take into account the error in the baseline or sigma. Given that each pixel is 0.9 arcseconds (see the Assessment of Basic Image Page) we find that UGC01810 is 2.24+/-0.03 arcminutes across the major axis. The diameter give by NED is 2.2 arcminutes.
Across Minor axis of UGC01810 The diameter here goes from where the arm crosses the sigma line (22+/-1) to where the bulge drops off and passes the sigma line (100+/-1). The diameter in pixels is 88+/-2 which translates into 1.32+/-0.03 arc minutes The diameter give by NED is 1.4 arcminutes.
Across fainter arms of UGC01810 I looked at this, not so much for measurement sake but to see the different levels of brightness in the two arms and whether the area between the arms was at all brighter than the background. It's mid level looks to be higher on average but it is still below the sigma line and so it's hard to tell for sure.
Across Major axis of UGC01813 (the smaller galaxy) The diameter here goes from 24+/-1 to 88+/-2 and so the length of the diameter in pixels is 64+/-3. This corresponds to .96+/-0.05 arcminutes. The value given by NED is 1.5 arcminutes
Across the Minor axis of UGC01813 This diameter goes from 26+/-1 to 44+/-1 which gives a width of 18+/-2 pixels. This translates into a diameter of 0.27 arcminutes NED's value for this diameter is 0.4 arcminutes.
Between the two galaxies Here I was looking to see if I could distinguish a bridge between the galaxies. It appears there is one though the value for the base line here doesn't appear to be correct. Even though it looks high the bridge still peaks over the sigma line.

Galaxy	Magnitude from LEDA	Measured Magnitude
UGC01810	13.5 +/-less than .3	15.882
UGC01813	15.2+/-less than 0.3	18.715

Galaxy	Magnitude from above mentioned source	Measured Magnitude
UGC01810	12.5+/-2.5	14.097
UGC01813	13.6+/-2.5	15.472

Across Major axis of UGC01810 (the larger galaxy) The diameter here goes from where the faint arm crosses the sigma line (34+/-1) to the same point on the farthest arm (167+/-1) and is 133+/-2 pixels. Note, the error here is simply the error in the measurement, it doesn't take into account the error in the baseline or sigma. Given that each pixel is 0.9 arcseconds (see the Assessment of Basic Image Page) we find that UGC01810 is 2.00+/-0.03 arcminutes across the major axis. The diameter from the POSS Red Print is 1.9 arcminutes.
Across Minor axis of UGC01810 The diameter here goes from where the arm crosses the sigma line (31+/-1) to where the bulge drops off and passes the sigma line (102+/-1). The diameter in pixels is 71+/-2 which translates into 1.07 arcminutes The diameter from the POSS Red print is 1.3 arcminutes.
Across Major axis of UGC01813 (the smaller galaxy) It was hard to determine which crossing of the sigma line to use and so I took two for each side. I will calculate the largest and smallest diameters. The diameter here goes from 27+/-1 to 94+/-1 or from 33+/-1 to 91+/-1. This gives a small diameter of 58+/-2 pixels and a large diameter of 67 pixels. These correspond to .87 arcminutes and 1.00 arcminutes respectivly. The diameter measured from the POSS Red print is 1.4 arcminutes
Across the Minor axis of UGC01813 The diameter here goes from 13+/-1 to 34+/-1 and gives a diameter of 21+/-2 pixels. This corresponds to a diameter of .315 arcminutes. The diameter measured from the POSS Red Print is 0.4 arcminutes.
Between the two galaxies We do see the bridge in this profile and so we can conclude that the bridge is made of older stars as opposed to younger stars.