The Methuselah Star – Oldest Star in the Milky Way

by Bill Pellerin

Object:  HD 140283, HIP 76976
Class: Metal Poor Sub-Giant Star
Constellation:  Libra
Magnitude:  7.26
R.A.:    15 h, 43 m, 1.86 s
Dec:    -10° 56’ 5.62”
Size/Spectral:  F3
Distance:  190 ly
Optics needed: A small telescope, binoculars

Here’s an odd one. I first heard of this star while watching a Great Course lecture in the series ‘The Life and Death of Stars’ by Keivan Stassun. Interestingly, to me, I had never heard of this star before, but it may be one of the more fascinating stars in the sky. The very early universe had much smaller quantities of the heavy chemical elements in it. Why? Because the heavy elements are created (fused, actually) in stars and in the early universe there had not been enough time for stars to form, live their lives, and seed the universe with these heavier elements. By ‘heavier’, I mean those elements in the periodic table beyond hydrogen and helium. This star has .4% of the quantity of heavy elements as our Sun (a 5 billion year old star).

So, any stars that are still around that formed in the early universe would be expected to have low quantities of these heavier elements. In fact, astronomers use the chemical contents of stars as a clue to the age of the star.

This star is deficient in these heavier elements that astronomers call ‘metals’ although these aren’t metals in the way we normally think of them. This low-metallicity star had to have begun shining in a very early era of the universe. Astronomers call this type of star a ‘Population II’ star (stars that formed much later are called ‘Population I’ stars… go figure). If you really want to investigate the earliest stars in the universe, these would be called Population III stars. For these stars there are no heavy elements at all; they’re all hydrogen and helium. No Population III stars have been identified.

It is relatively bright to earth-based observers because it is relatively close to us (as these things go) at 187 light-years. Astronomers now know that the age of the universe is 13.8 (latest estimate) billion years old. Interestingly, the age of this star is estimated at 14.46 +/- .8 billion years, so the low end of the range is 13.66 billion years. While there’s some uncertainty in the age, clearly the star can’t be older than the universe. What we can say for sure is that this was an early forming star.

This star also has a very high proper motion. Proper motion is its real motion across our sky and this star is moving at .13 milliarcseconds per hour, about 11.4 arcseconds in a year. This amount of motion could easily be detected astrometrically by amateurs. It would be fun to image the star field today, and do the same again and see the proper motion of the star.

This is a low-mass star with only about 85% of the mass of our SunNot until the ‘helium flash’ event at the end of the red giant phase does helium begin burning. Remember that the lower the mass of a star the longer it lives, and this one is an example of such a low mass star. It’s not a main-sequence star any more, and it’s not yet a red giant star, but it’s on the path leading from the main-sequence to the red-giant phase. Even though the star has moved off the main sequence, it’s still burning (fusing) hydrogen to helium. The age of the star is inferred from its position on the HR (Hertzsprung-Russell) diagram employing standard stellar evolution models.

For HAS observers, you’ll want to catch this one early in the evening in September. By mid-month it sets at about 22:45. It’ll be an easy observation, though, and one you can catch just after you get your telescope set up or your binoculars out of the bag.

by Rene Gedaly

We want YOU on the 2017 Membership team!
Want to meet more of your fellow members? Be one of the next smiling faces at the membership table for 2017! We'd like to get a group of three or four together who can take turns greeting folks at the badge table. Contact Ed Fraini at vp@astronomyhouston.org for more.

We won! Horkheimer/O'Meara Journalism Award
HAS student member Clay Parenti won the Astronomical League's Horkheimer/O'Meara Journalism Award with his essay on “Finding the Cosmic Order: The Story of Kepler’s Laws of Motion.” His award will be announced in the September Reflector. Congrats, Clay!

Establishing youth group membership
Youth and school groups continue to find us on the web and we welcome them as the potential new members they are. It's a big enough uptick in requests, though, that it's time investigate creating a new membership category. Education & Outreach Co-chairs Joe Khalaf and Debbie Moran are on it.

Sharing Science with Any Audience
In the same vein, it may be time to develop mutually beneficial relationships with other groups in the community. The leadership team has identified a short list of community, policy, and media groups for me to target at the Sharing Science with Any Audience workshop at Texas A&M this month ...

By Bill Pellerin

Object:  P Cyg
Class: Luminous Blue Variable
Constellation:  Cyg
Magnitude:  4.8
R.A.:    20 h, 17 m,  47 s
DEC:    38°  01’ 59”
Size/Spectral:  B1
Distance:  6500 +/- ly
Optics needed: A small telescope to pick this star out in a crowded field.
This star has a Bayer designation, ‘P’, but, as is often the case, the star is a variable but it retains its Bayer name. The naming convention for variable stars is different; the first variable in a constellation is typically called ‘R’. You can also find P Cyg using the following catalog names: SAO 069773 or HD 193237. Not much attention has historically been directed to a 5th magnitude star in a crowded field of stars, but in the year 1600 the star had the audacity to brighten to about 3rd magnitude, six times brighter than it was, and now is, at 5th magnitude. Over the time that this star was observed it brightened and dimmed a few more times. If you look at the data on the star today (AAVSO.org) you’ll find that it has dimmed and brightened (over a period of a few days) by a fraction of magnitude, hard to detect visually, but easy to detect photometrically ...

by Mike Edstrom

STELLAR SUMMER ACTIVITIES The sides of the new bunkhouse are all in place, a few of the roof rafters are left to put up, great progress is being made.  We look forward to completely enclosing the bunkhouse so we can install the air conditioners and work in a cooler place, more to come.

It was a very busy late June and early July at the Dark Site; you should have seen Rene’s article about the Girl Scouts visiting on June 24th and 25th. Then on June 30th and July 1st we hosted a group of 22 7th to 10th grade students and 7 chaperones from Eddie V. Grey Wetlands Center in Baytown, TX. We had several HAS members: Rene Gedaly, Allen Wilkerson, Ed Fraini, Don Selle, Steve and Amelia Goldberg, Brain Cudnik and myself using the three observatory scopes, Allen’s Meade, Ed’s dob, Amelia’s dob and my observatory to show them planets and several Messier objects once the clouds cleared. I was very impressed as the students stayed up very late as many of them just laid on the ground in the observatory parking lot looking up and said they had never seen so many stars. It made the effort we all put into the evening worthwhile ...