September 19, 2018

AstroChallenge: The Sub-Giants of Delta Serpentis.

You might’ve noticed that we here at Astroguyz have a “thing” for double stars. This can be a controversial affliction among deep-sky observers, as many an astro-imager sees mere “stars” as boring compared to their quest for faint nebulae and galaxies. But for many an observer trapped in the ‘burbs, double stars offer a deep sky target that still holds up well under light polluted skies when those +14th magnitude galaxies just don’t stand a chance of ever shining through. This week, we look at the fascinating system of Delta Serpentis.  This yellow white pair is 210 light years distant in the constellation Serpens Caput (The Head of the Serpent). A complex system, the bright pair has 4.1” arc seconds of separation & magnitudes +4.2 (Component A) and +5.2 (Component B), respectively. Position angle of the A-B pairing is 178°. Also, sharp-eyed viewers may be able to catch another associated pair 66” distant at position angle 14°, with 14th and 15th magnitude components with a 4.4” arc second spread.  The A and B components are both F-type sub-giants off of the main sequence shining at 76 and 31 times the luminosity of our own Sun. The primary pair is embraced in a 3200 year orbit, while the distant has an unknown period.

Delta Serpentis: A finder chart. (Created by the Author in Starry Night).

The position for the system is as follows;

Right Ascension: 15 Hours 34.8’

Declination:  +10° 32’

The pair is well positioned to the west after sunset for the next month…good luck, and let us know of your triumphs and tales of hunting down double-star prey!

The Astro-Word of the Week is Delta Scuti Variable. Also sometimes referred to as a Dwarf Cepheid variable stars, this is a rare form of variable of which the A component of Delta Serpentis is a “card carrying” member. Hey, you knew something was special about the pair, right?  Lesser known than traditional Cepheids, these smaller F-type stars also have a period-luminosity relationship and also serve a crucial standard candles. Credit for discovery of the variability of the prototype Delta Scuti goes to a paper written by W. W. Campbell and W.H. Wright in 1900. Drawings depict Delta Scuti as far back as Flamsteed’s 1781 southern sky star catalog.  These stars occupy a remarkable branch of the Hertzsprung-Russell diagram; a metal poor branch of instability near the center of the traditional “lazy-S” curve. Most of these stars are between 1 and 2.5 solar masses and have a very short range of variability of 0.03 to 0.3 days.   Why study Delta Scuti variables? Well, astrophysical modeling on these stars has proven crucial to the emerging field of astro-seismology. Delta Scuti-style variables can be further divided into high amplitude and low amplitude variables. This fast variability characteristic coupled with an asymmetric non-radial pulsation enables astronomers to map and model “star-quakes” within the interior of Delta Scuti type stars much the same as helioseismologists study acoustic waves resonating through our own Sun.  Backyard observers have also gotten into the act, and some suspected Delta Scuti type variables awaiting validation include V703 Scorpii, YZ Bootis, and CY Aquarii. These swiftly evolving F-type stars do not reside in the instability region of the H-R diagram for long relative to their lifetimes, a prime reason that this particular class of variable stars is comparatively rare in the sky. It’s amazing that we can glean so much information from a few photons of light!

 

07.02.11: Seeing the Sun in STEREO.

Amid the Super Bowl madness that was this past weekend, a quiet milestone was reached in the realm of Spaceweather; NASA’s twin Solar Terrestrial Relations Observatory (STEREO) spacecraft achieved a 360 degree coverage vantage point in respect to our sun.

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17.9.9: A Farside Sunspot Group?

Activity on the Sun may be finally picking up. Specifically, a new sunspot group has been “seen” up forming on the farside of the Sun. That’s right; astronomers can now model the goings-on within the Sun with such precession, thanks largely to satellites like SOHO and the GONG network, that we can now predict with some confidence whats going on on the side of the Sun turned away from us! This is mostly due to a growing sub-branch of astronomy known as helioseismology. The Sun itself rotates at about once every 25 days, although this varies by latitude because the Sun is essentially a big rotating gas ball. The twin Stereo spacecraft are also slowly inching their way out into leading and trailing orbit(s), providing us with a good “peak” around the limb. If you own a solar scope, the next week or so might be good cause for increased monitoring; the new solar cycle #24 might just be ready to put on its first show!

 

Event of the Week: 29.06.09: The Deepening Solar Minimum.

Something mildly bizarre is happening on our nearest star, the Sun. Or should we say, a lack there of… This weeks astro-event is a sort of non-event, but one of the big mysteries of 2009; where exactly are the sunspots? Turning that newly constructed white-light filter we built last week on our mild-mannered star shows a definite lack of activity in the solar photosphere. This isn’t entirely abnormal, as the Sun is just coming off of a solar minimum that occurs every 11 years. What is unusual is the length of this minimum; we’ve had over 600+ spotless days since 2004, a quarter of which have been in 2009 alone. A typical minimum consists of an average of 485 days. You have to go way back to 1913 to find such comparable a lull! Two tiny sunspots appeared last week, which prompted the discussion as to whether the latent solar cycle #24 is finally amping up or not. Both spots belong to the new cycle, their reversed polarity giving them away. Using the technique of helioseismology, Frank Hill and Rachel Howe at Tucson’s National Solar Observatory have discovered that the Sun’s internal dynamo isn’t dead, just sleeping. They predict that the subsurface tachocline should begin intersecting the surface at the junction of 22 degrees latitude by the end of 2009, and activity should resume. It’ll be a wait and see mystery that will only deepen if the spots don’t return to roost; and does this portend a stronger than usual maximum around the solar bend? Stay tuned!

This week’s astro-term of the week is Sporer’s Law. First worked out by astronomer Gustav Sporer, this law simply states that sunspots form at higher latitudes at the beginning of a solar cycle, and then gradually progress downward to lower latitudes in both hemispheres as the cycle progresses. We never see spots above 45 degrees of latitude, and astronomers aren’t quite sure why. The link between the solar cycle and the climate isn’t yet fully understood. Could a spotless Sun mimic or mask the effects of global warming? Both Earth and space bound telescopes are keeping a constant watch on our Sun. Cries of another Maunder minimum, a time from 1645 to 1715 that was marked by harsh winters and almost no sunspots were seen, may be a bit premature… cycle #24 were art thou?