48-minute time-lapse animation of main belt asteroids (41) Daphne and (1369) Ostanina as imaged through an Orion ST-80 telescope with ZWO ASI482MC camera. Also shown is the active galaxy Markarian 937. The animation consists of seven images, each a stack of 12 @ 60 seconds. Field of view is approximately 60 x 40 arcminutes. North is up. East is left. Click on the image for a larger version in a separate window.
As previously mentioned, the night of November 6-7 was a three-target night. I’ve already posted about the first target, (1278) Kenya. The second and third targets came together as a pair in the same part of the sky. The pair consisted of main belt asteroids (41) Daphne and (1369) Ostanina. Also, as noted in my earlier post, this session was part of an ongoing trial of using my Orion ST-80 telescope for imaging brighter main belt asteroids.
The seeing for this part of the session continued to be poor, but quickly deteriorated to extremely poor with high thin clouds moving in overhead. Finally, with the starfield brightening and dimming so much that the guidescope was unable to maintain its lock on guide stars, the session was scrubbed with a little less than one hour of usable imaging data. Just enough data was salvaged, however, to show some asteroid movement against the background star field. Despite the poor imaging conditions, a small faint bonus object, Markarian 937, showed up just above the background noise in the salvaged images. More about it below.
The cropped images below show each asteroid’s actual sky movement alongside a finder chart produced by the Lowell Observatory’s online Asteroid Finder tool. Click on each image for a larger version in a separate window.
(41) Daphne
The immediate field around (41) Daphne with a finder chart showing its predicted position and movement during a three hour period encompassing the 48 minutes of this animation. The chart was produced with the Lowell Observatory’s online Asteroid Finder tool. Field of view approximately 30 x 30 arcminutes. North is up. East is left.
(1369) Ostanina
The immediate field around (1369) Ostanina with a finder chart showing its predicted position and movement during a three hour period encompassing the 48 minutes of this animation. The chart was produced with the Lowell Observatory’s online Asteroid Finder tool. The active galaxy Markarian 937 shows up very faintly at V magnitude 15.5. Field of view approximately 30 x 30 arcminutes. North is up. East is left.
Sky Movement and Magnitude
During this session, both asteroids were moving across the sky against a background of stars in the constellation Pisces.
As predicted by the Minor Planet Center, (41) Daphne was moving at 0.27 arcseconds/minute toward 233.4°. And, (1369) Ostanina was moving at 0.19 arcseconds/minute toward 207.7°.
The measured V magnitudes for both objects was close to the Minor Planet Center’s predicted magnitudes as shown in this table:
| Asteroid | V mag (measured) |
V mag (predicted) |
| (41) Daphne | 12.7 | 13.0 |
| (1369) Ostanina | 15.3 | 15.2 |
More About (41) Daphne and (1369) Ostanina
(41) Daphne and (1369) Ostanina are main belt asteroids that orbit the Sun between the orbits of Mars and Jupiter. On this night, (41) Daphne was 2.5 AU from Earth and 3.3 AU from the Sun. (1369) Ostanina was closer to us at 1.9 AU and 2.8 AU from the Sun.
Even though (41) Daphne was more distant than (1369) Ostanina, it appears much brighter in these images because it a much larger object. With a diameter of 205 km, (41) Daphne is nearly five times the size of (1369) Ostanina, which is only 42 km in diameter. As a much larger object, (41) Daphne reflects more sunlight and therefore appears brighter.
Markarian 937
As mentioned above, this session was another test of using my small Orion ST-80 telescope for imaging bright main belt asteroids. As part of the testing, I have been trying to gauge the limiting magnitude for one-minute exposures using this telescope and ZWO ASI482 camera. Although some of the image processing tools I’ve been using indicate a limiting magnitude of 15.7-15.8, it is always helpful to have objects of known magnitude in the image for additional confirmation.
After finding out that Markarian 937 was in the field of view, I researched its magnitude and was surprised to find out that eleven different catalogs and surveys gave very different V magnitudes for it. The magnitudes varied from the bright end at 13.2 to 16.0 at the faintest. This is quite a discrepancy. At worst, discrepancies on the order of 0.5 – 1.0 might be expected, but nearly three full magnitudes is a bit much. Using the astrometry-photometry program ASTAP, I measured Markarian 937’s V magnitude as 15.5 on my images. V magnitude 15.5 is very close to the 15.7-15.8 limiting magnitude derived from analysis of images from previous sessions. And Markarian 937 certainly looked this faint on my images.
After digging a bit deeper, I’ve settled on a guess as to why the different reference sources report such divergent magnitudes for this object. It turns out that Markarian 937 is a Seyfert galaxy. Seyfert galaxies are one of two types of so-called active galaxies, the other being quasars. Active galaxies, or their nuclei, are known to vary in luminosity over periods of days, months, or years. So, I think it might be reasonable to infer that Markarian 937’s three-magnitude variation might be attributable to actual changes the luminosity of its nucleus over the span of years covered by the different surveys that measured its magnitude in the V band.
I don’t claim to have any great expertise in this area, but that’s my working hypothesis. Mystery solved?
Full details for this session follow.
Observation Details
November 7, 2023 04:48:56-05:36:30 UT
Seeing: Poor-Extremely Poor Transparency: Poor Sky Condition: Bortle 7
Location: Edmond, Oklahoma USA
Image Details
48-minute time-lapse animation. Originally planned for 1.5-2.0 hours, but session cut short by deteriorating seeing and clouds.
5 images, each a stack of 12 @ 60 seconds (total integration per image 720 seconds/ 12 minutes).
Gain 250
FOV:
- Animation 1, asteroids 41 & 1369, 800×500: 61.7 x 38.5 arcmin / 1.03° x 0.64° (cropped from original 1920×1080, 98.5’x55.4’ / 1.64°x 0.92°; original scale 3.08 “/pixel)
- Animation 2 asteroid 41, 400×400: 30.8 x 30.8 arcmin / 0.51° x 0.51° (cropped from original 1920×1080, 98.5’x55.4’ / 1.64°x 0.92°; original scale 3.08 “/pixel)
- Animation 3 asteroid 1369, 400×400: 30.8 x 30.8 arcmin / 0.51° x 0.51° (cropped from original 1920×1080, 98.5’x55.4’ / 1.64°x 0.92°; original scale 3.08 “/pixel)
North up. East left.
Equipment
Telescope: Orion ST-80 (80 mm f/5) + Orion Field Flattener + Baader Fringe Killer Filter
Camera: ZWO ASI482MC
Guide Scope: SVBONY SV165 (30 mm f/4)
Mount: Celestron CGEM
Image Capture & Processing
Capture: SharpCap Pro
Guiding: PHD2
Process: Deep Sky Stacker, GIMP
Astrometry/Photometry: ASTAP, Tycho Tracker
NOTE: January 23, 2024. Post edited and re-formatted.