SKYLIGHTS: Star of the Week

[MargaritaMc]

Star of the week for the week starting Friday, January 2, 2014

Jim Kaler writes:
Yay, we are back to weekly, at least for a time, and best wishes for the coming year.

STAR OF THE WEEK: PSI PER (Psi Persei). Famed are the Pleiades and Hyades of northern fall and winter. But who pays attention to another large and bright open cluster, the Alpha Persei cluster that surrounds the brightest member, Mirfak, a second magnitude supergiant? The problem is that the cluster is so spread out within the surrounding Milky Way that it does not quite look like a real assembly.
Just 2.6 degrees southeast of Mirfak, we run into the brightest "main sequence" (hydrogen-fusing) member of the cluster, the fourth magnitude B5 dwarf Psi Persei... The really big thing about Psi Per is its great equatorial rotation speed of at least 367 kilometers per second (the axial tilt not known), which gives it a rotation period of under 0.87 days. No surprise then that Psi Per is one of the brighter "B-emission" stars in the sky, one that has created for itself a surrounding fat disk that changes with time...

M

[MargaritaMc]

I'm also posting an excerpt from Skylights proper this week, as this info was new to me:

Astronomy news for the week starting Friday, January 9, 2015.
This week centers on the third quarter Moon, which takes place on Tuesday, January 13, shortly before daybreak in North America, allowing a near-perfect quarter phase to be seen. Look for the star Spica in Virgo just to the south. In the third century BC, Aristarchus of Samos tried to measure the angle between the Sun and Moon at the time of the quarter. If the Sun were infinitely far away, the angle would be 90 degrees. He found an angle of 87 degrees, and concluded that the Sun was 20 times farther than the Moon. It turns out that the angle is impossibly small to find with the naked eye and he was off by a factor of 20 (the Sun 400 times farther than the Moon). But his brilliant conclusion that the Sun is much more distant than the Moon was indeed correct. ...


STAR OF THE WEEK: CHI CET(Chi Ceti, plus HD 11131). Half a degree southwest of fourth magnitude Baten Kaitos (Zeta Ceti), one of the stars that outlines the Sea Monster of the Andromeda myth, lies fifth magnitude (4.67, almost fourth itself) Chi Ceti. One immediately thinks, aha!, a naked-eye double. But no, Chi Ceti is fairly close to us, 75.2 light years (give or take just a half), whereas Zeta is three times as far, the alignment just a coincidence, as so often seen. A closer look, though, shows another, fainter star of seventh magnitude (6.75), HD 11131 of the Henry Draper spectral catalogue, just 3.2 minutes of arc to the west that is 74 light years away (with an uncertainty of 5). Also called Chi Ceti B, could it belong to the brighter star? ...

[Ann]

Thanks, Margarita, for posting all these SKYLIGHTS: Star of the Week posts!

I loved reading about Psi Persei, since I really love the Alpha Persei moving group (or cluster)! And Psi Per is the greatest main sequence star in there. (And it's blue, of course!)

I also found it absolutely fascinating to read about Chi Ceti and HD 11131, if only because I recently argued so vehemently that HD 176269 and HD 176270 in Corona Australis make up a binary pair. Chi Persei and HD 11131 have some very interesting characteristics in common with HD 176269 and HD 176270: their colors and magnitudes combined with their spectral classes and great proximity in the sky argue strongly that they are the same distance from us and belong together. But in the case of Chi Ceti and HD 11131, they are really quite close together but not gravitationally bound.

Fascinating! Thanks again, Margarita!

Ann

[MargaritaMc]

I'm really pleased that someone other than me reads them!
M

[MargaritaMc]

Star of "the week" for the two weeks starting Friday, January 16, 2015.

Jim Kaler writes:
Back to fortnights for a bit: thanks for your patience. The next skylights will appear January 30, 2015.
...
STAR OF THE WEEK: PHI PER (Phi Persei). An amazing star, Phi Persei is an extreme system that inspires more than a bit of awe. Not part of any of Perseus's usual outlines, mid-fourth magnitude (4.07), Phi Per is just barely over the border with Andromeda and about midway between the classical figures of Perseus and Cassiopeia, so it's easy to miss, and that's too bad. .... It's a hot class B (B2) hydrogen-fusing dwarf, an emission-line star with a surrounding radiating disk in the mold of Gamma Cassiopeia and Zeta Tauri, indeed a "shell star" in which the disk is presented more or less edge on. Consistently, Phi Per is spinning madly, with an equatorial velocity of at least 430 kilometers per second, making it one of the fastest-rotating stars known. ...

Phi Persei has a fascinating companion, a hot subdwarf "O" star. Read Jim's piece at his site to find out more.

Margarita

[MargaritaMc]

Star for the two weeks starting Friday, January 30, 2015.

The next skylights will appear February 13, 2015.

STAR OF THE WEEK: HR 1035 CAM (HR 1035 Camelopardalis). Camelopardalis, the Giraffe, browses quietly, surrounded to the south by bright Cassiopeia, Perseus, and Auriga, its pasture on the other side extending nearly to the North Celestial Pole. But you'd be a bit pressed to find it as the brightest star of the sprawling constellation is fourth magnitude (4.03) Beta Cam. The number two star, fourth magnitude (4.21) HR 1035 (the name from the Bright Star Catalogue) does not even have a Flamsteed number (which it ought), let alone a Greek letter (Alpha Cam ranks third, Gamma sixth). One would hardly recognize HR 1035 then as one of the great stars of the local Galaxy, a white class B9 bright supergiant and the brightest star of the Cam OB1 association of hot (O and B, and many others of lesser rank) stars, just a bit brighter than its constellation-mate and near-neighbor, HR 1040 Cam. The distance is so great as to be quite insecure, parallax making it 1940 light years away but with uncertainties that may take it as far as 2760 l-y or as close as 1500. ...

M

[Ann]

I love the area around HR 1035 and HR 1040. The reflection nebulas around the these mighty stars are lovely. There is a bit of emission nebulosity in the area too, as is seen in this beautiful image by Adam Block.

And personally I think that a star of spectral class B9 should be called blue, but you know me...

It was interesting as always to read about the star of the week, so thanks again, Margarita (and Jim Kaler)!

Ann