Cor Caroli

 Cor Caroli (Alpha Canum Venaticorum) is the brightest star in the constellation Canes Venatici (Hunting Dogs).  It is an easy and attractive double star for small telescopes.  

credit: IAU (CCA 4.0 International license)

 

Cor Caroli.  E-M5 + Rokinon 135mm f/2.  ISO 800, 30 s. 2° FOV.

The two component stars have magnitudes 2.8 and 5.6 and are separated by 19 arcsec.  They were easy to photograph with a Sky-Watcher SkyMax 102 amplified by a 2.5x Tele Vue Powermate.

Cor Caroli: α² and α¹. E-M5iii, ISO 800, 1 s.  FL = 2781 mm.

With a TS-Optics 50mm ED f/4.2 telescope and a Tele Vue Nagler T6 9mm eyepiece (23x) I was able to visually separate the two stars very easily.  A higher-power view with a Celestron Xcel-LX 5mm eyepiece (42x) was even better. 

In the Cambridge Double Star Atlas (2nd Ed) by MacEvoy and Tirion these stars are listed as spectroscopic binaries, but there is reason to doubt this description.  For the primary, at least, this was pointed out by Otto Struve in 1942 (Proc. American Philosophical Society, Vol. 85, p . 349–358, 1942).  The brightest of the pair (designated α² CVn) has one of the highest known magnetic fields for a main-sequence star.

TS-Optics 50mm ED with 9mm Nagler

with the 5mm Xcel-LX

Eclipse preparation

 I am 99% certain that I won't be driving 12 hours to Texas to join millions of my closest friends to view the eclipse on 8 April.  Instead I will make do with the 73% coverage that will be visible here in Santa Fe.  Yesterday and today I did some test images to get my camera settings dialed in.  The telescope was an Orion 80mmED with a  Lunt solar wedge and a ND-0.6 filter.

28 March.  E-M5iii, ISO 200, 1/800 s.

29 March.  E-M5iii, ISO 200, 1/1000 s.

There is a large and active sunspot group that is about to rotate out of view around the western limb.  Counterintuitively, this is a dangerous position for solar flares.  A phenomenon known as the "Parker Spiral" causes charged particles to follow a magnetic flux spiral backward toward Earth. There was a radio blackout over the Pacific Ocean yesterday caused by a solar storm from this sunspot.

A 2x enlargement

Multiple multiple-star systems

The motivation for this imaging session was to see if I could successfully record the companion star to Polaris (answer: yes).  This multiple star is a moderately-challenging  visual double for small telescopes. The equipment used was a Sky-Watcher Skymax 102 MCT (Maksutov-Cassegrain Telescope) amplified with a Tele Vue 2.5x Powermate.  The nominal base focal length for this scope is 1300 mm (L/D = 12.7).

Prior to setting up the camera, I first did some visual tests with several different eyepieces without the Powermate amplifier.  The eyepieces used were: Tele Vue 24mm Panoptic, Takahashi TPL 12.5 mm, Masuyama MOP 10mm, and a Brandon 12mm.  

The 24mm Panoptic (54x) was used as a "finder" eyepiece.  With some concentration I was able to see the companion star with this eyepiece, in spite of the relatively low magnification.  The star was visible with only occasional lapses with the Takahashi TPL (112x).  I was never certain about seeing it with the Masuyama (130x).  The best and steadiest view was with the Brandon (108x).  The Takahashi and Masuyama eyepieces are recent offerings in the market and consequently the subject of much comparison and discussion on astronomy forums.  Brandon eyepieces have been around since the 1950s and are revered by some and dismissed by others.  On this night, the Brandon came out ahead.

Polaris, Alpha Ursae Minoris, the North Star or Pole Star, is a triple-star system.  The magnitude-2 primary star Polaris Aa has a close companion Polaris Ab separated by less than 0.2 arcsec.  This companion is 420 times fainter than the primary and has been imaged by the Hubble Space Telescope. The  more easily-visible companion is Polaris B.  It has magnitude 9.1 and it separated from Polaris A by 18.6 arcsec.  Polaris B is seen below and to the right of Polaris A in the image below.

Polaris A+B.  E-M5iii + SW102 + 2.5x Powermate.  ISO 800, 5 s.

The nominal focal length of the SW102 + 2.5x Powermate is 1300 × 2.5 = 3250 mm.  However, that applies only to a specific focal-plane position.  Moving-mirror telescopes such as this one are focused by shifting the focal plane rather than the eyepiece or image sensor.  That changes the effective focal length.  I determined the effective focal length of the present setup by measuring the separation between the double-star pair Mizar and Alcor in Ursa Major.

Mizar and Alcor.  ISO 800, 4 s, 4x binning.

The angular separation of the two stars is 0.1968°.  In the E-M5iii image they are separated by 2895 pixels.  This works out to L = (0.0033 mm/pixel)*(2895 pixels)/tan(0.1968) = 2781 mm for the true effective focal length and an image scale of about 0.245 arcsec/pixel.

Mizar is an easy visual double star in small scopes, and each of the two components is itself a double, as is Alcor.  This is therefore a six-star system.  It is the second-closest sextuple star system, about 86 ly distant.

Mizar A + B.  Each star is also a double.  ISO 800, 1 s + 0.5 s average.

The closest sextuple star system is Castor, Alpha Geminorum, at a distance of about 51 ly.  The two brightest components, each of which is a spectroscopic double, are currently separated by just over 6 arcsec.

Castor A+B.  ISO 800, 1/4 s.  Stack of 4 images.

The third component, Castor C, also known as YY Geminorum, is separated by 73 arcsec.  This magnitude-8.8 companion requires a longer exposure to be visible.  Castor C is an eclipsing binary system of two red dwarfs.

Castor C (YY Gem) is the reddish blob to the left and up from the overexposed primary. ISO 800, 4 s.  North is to the right.

 Although Castor is designated Alpha Geminorum, it is slightly fainter (mag 1.6) than its twin Pollux, Beta Geminorum (mag 1.2).
 

Castor (top R) and Pollux (bot L).  E-M5 + Rokinon 135mm f/2 + softon filter.  ISO 1600, 30 s.

The "Trapezium", also known at Theta 1 Orionis, is an asterism of four stars at the heart of the great Orion Nebula, M42.  The component stars are part of a tight open cluster associated with this nebula and are too closely packed to be in a gravitationally stable arrangement.  They will eventually disperse.  The brightest one will  go supernova in a few million years.

Theta 1 Orionis, the "Trapezium".  ISO 800, 1 s.

Some summer Milky Way highlights - Creede, 2022

 The summer Milky Way has an abundance of targets for binoculars and small telescopes.  This is the view from Bristol Head Acres at 9 pm on 28 Aug 2022:

Sony A7 + Rokinon 24mm f/1.4 + softon filter.  ISO 1600, 30 s. sqml = 21.45

The white ellipse in the image below highlights a region of interest for some following pictures.  Near the top of the ellipse are the Eagle Nebula (M16) and the Omega Nebula (M17).  In the middle is the Small Sagittarius Star Cloud (M24).  Near the bottom are the Lagoon Nebula (M8) and the Trifid Nebula (M20).  There are so many other named objects in this region that it would be difficult to point to all of them

The next image was obtained in the late evening of 23 June.  My observing notes record a sky brightness of sqml=21.68, which is very dark.  In the lower right is the Small Sagittarius Star Cloud (M24), the Omega Nebula (M17) is in the middle, and above that is the Eagle Nebula (M16).

E-M5iii + Rokinon 135mm f/2.  ISO 1600, 60 s.

The Eagle Nebula (M16) is in the upper half of this cropped image.  It is an active star forming region that contains a cluster of young stars.  This is the location of the famous Hubble Space Telescope "Pillars of Creation" image.  It is about 7000 ly distant.

The Omega Nebula (M17) in the lower half of this image is about 5000 ly distant.

The Small Sagittarius Star Cloud (M24):

 In the upper right corner of this next image is the star cluster M23.  The Lagoon Nebula (M8) is near the bottom.

E-M5iii + Rokinon 135mm f/2.  ISO 1600, 60 s.

In this cropped image, from bottom to top are: Lagoon Nebula (M8), the Trifid Nebula (M20), and above and to the left of that is the star cluster M21.

The Lagoon Nebula, M8

The Trifid Nebula, M20, and M21

M23

Omega Nebula, M17

M16. 2x upscaled. The white circle is the approximate location of "Pillars of Creation".

 

A large but overlooked asteroid: (704) Interamnia

 I was looking at a list of the largest asteroids and was surprised to see one that had previously escaped my attention: (704) Interamnia.  The largest asteroid is (1) Ceres, which is also now classified as a dwarf planet.  The next three are (4) Vesta, (2) Pallas, and (10) Hygiea.  Interamnia is number 5, the fifth largest asteroid, with a mean diameter of 332 km, about one third the size of Ceres.  Interamnia was discovered in 1910, over 60 years after the discovery of the fourth largest asteroid, Hygiea (1849).

As it turns out, Interamnia is currently very close in the sky to Vesta, which I have recently photographed.  So I went back to the photos of Vesta and found it within the same field-of-view (FOV) near the edge of the frame.   The image below was taken on 1 March with a Rokinon 135mm f/2 lens.  The horizontal FOV is about 5.5°. 

The white circles mark M1 (Crab Nebula), Vesta, and Interamnia.

Vesta is the brightest asteroid and is periodically bright enough (mag 5.2) to seen with the unaided eye from a dark-sky location.  Interamnia, on the other hand, never gets brighter than magnitude 9.9.   At the time this image was taken, Vesta was at magnitude 8.0 and Interamnia was magnidute 11.8.

Last night (10 Mar) I went out and deliberately targeted Interamnia.

(704) Interamnia.  E-M5 + Rokinon 135mm f/2.  ISO 800, 30 s. 2° FOV.

Here is an expanded (3x) view.  Interamnia, marked by the white lines, is passing just below a magnitude 13.2 background star.

This region of the sky has many star clusters.  Here is a finder chart for 10 March:

credit: SkySafariAstronomy.com

Between the two asteroids and the large Hyades cluster are two small open clusters: NGC 1746 and NGC 1647.  

NGC 1746.  E-M5 + Rokinon 135mm f/2.  ISO 800, 30s.

NGC 1647.  E-M5 + Rokinon 135mm f/2.  ISO 800, 30 s.

For all of these images I was using the ZWO AM3 mount, unguided.  As usual, click to get access to the full-size versions.

A comet, some asteroids, some star clusters

Periodic comet 12P/Pons-Brooks is appearing on news sites because of the expectation that it will be visible during next month's solar eclipse.  It is currently heading toward perihelion on its 71-y orbit.  It is difficult to catch in the early evening twilight, especially from my site in urban Santa Fe.  I was just able to get a few images before it set into the neighbor's trees behind the backyard fence.

For this image I chose a Sigma 56mm f/1.4 lens with an Olympus E-M5iii camera.  The intent was to use a field-of-view (FOV) wide enough to show the comet and the Andromeda galaxy in the same frame.  The galaxy is circled in the upper right, the comet in the lower left.  The image is tilted because the camera was riding on the ZWO AM3 equatorial mount rather than being leveled to the horizon.

E-M5iii  + Sigma 56mm f/1.4.  ISO 800, 30 s.

 

Here is a close up of the comet, same image file, just processed differently:

comet 12P/Pons-Brooks, 05 Mar 2024.

The comet shows the typical green glow from diatomic carbon and cyanogen.  It is just possible to see a faint tail extending upward to the right for about 1°.

After twilight faded and it got as dark as it gets here (sqml=19.55), I turned the camera to a few other objects.

Aldebaran and the Hyades.  E-M5iii + Sigma 56mm f/1.4 + softon filter.  ISO 800, 30 s.

The region just north of Orion is interesting, with two star clusters (Cr 65 and Cr 69) and the asteroid (4) Vesta passing through:

E-M5iii + Sigma 56mm f/1.4 + softon filter.  ISO 800, 30 s.

Here is a close-up of Cr 65 (Collinder 65):

Collinder 65

A little bit farther north in the sky it was possible to frame three of the major asteroids: (4) Vesta, (5) Astraea, and (9) Metis.   The best way to view this image is to click on it and zoom-in on the full-size version (as usual).

Vesta was discovered in 1807 and is currently at magnitude of 8.1. Astraea was discovered in 1845 and is at magnitude 10.9.  Metis was discovered in 1848, and is at magnitude 10.4. 

Two evenings later (07 Mar) I set up a different lens: a Tokina 400mm SD f/5.6 manual focus telephoto. I don't know the exact age of the lens because I bought it used, but it probably dates back to the late 80's or early 90's.  For these exposures I also used a Metabones Speedbooster 0.71x reducer.  This combination yields a focal length of 284mm at f/4.  The Speedbooster required some tweaking to achieve infinity focus.  Focus was confirmed with a Bahtinov mask.

Collinder 69, 2° FOV..  E-M5iii + Tokina 400mm SD + 0.7 Speedbooster.  ISO 1600, 30 s.

M35, 1° FOV.  Same settings as previous image.

There is chromatic fringing with this lens, which manifests as bloated pink stars in this image of the Orion Nebula.  Even so, I like some of the results.  The last time I used this lens was during the annular eclipse last October. I look forward to trying it under the dark skies of Creede.

 

More time with the ZWO AM3 mount

Some clear and moonless evenings have allowed me to experiment further with the ZWO AM3 harmonic drive (strain wave) mount.  I am also still evaluating the 0.8x reducer/corrector with the AT72EDII f/6 refractor.  With this reducer in place the effective focal length is 346mm at f/4.8.

M1 (Crab Nebula).  E-M5iii, ISO 1600, 30 s.

M42 (Orion Nebula). E-M5iii, ISO 1600, 30 s.

(04) Vesta.  E-M5iii, ISO 1600, 30 s. 2° FOV.

 At magnitude 8.0, the asteroid (04) Vesta should be visible with binoculars, but the Santa Fe sky brightness (sqml=19.53 last night) is an impediment.  It is currently about 2.5° from the Crab Nebula in the constellation Taurus and situated high in the early evening sky.

Vesta was discovered in 1807 by German astronomer Heinrich Olbers.  It was the fourth asteroid discovered, after Ceres (1801), Pallas (1802), and Juno (1804).  Olbers was also the discoverer of Pallas and is known for Olber's Paradox, which asks "Why is the night sky dark?".

Vesta is the second largest asteroid after Ceres, which is now classified as a dwarf planet.  The movement of Vesta against the background stars is easy to record:  Here is an animation of three exposures obtained over three nights (28-29 Feb, 01 Mar):

Movement of Vesta, 28 Feb - 01 Mar  1° FOV.

In this image Vesta is moving West to East (right to left).  The third image in this sequence was obtained with a Rokinon 135mm f/2 lens and E-M5 camera.
 

 It was 38 years more until the discovery of the fifth asteroid, (05) Astraea, in 1845.  Astraea is currently at magnitude 10.2 in the northern part of Orion, about 8.5° from Vesta.

(05) Astraea, 29 Feb 2024.  E-M5iii, ISO 1600, 30s.  2° FOV.

Here is a two-night (29 Feb - 01 Mar) animation of Astraea's motion:

AT72EDII and Rokinon 135mm.  1° FOV.