#cepheid variables

[livingforstars]

The Cepheids of M100 - January 10th, 1996.

"Can this blinking star tell us how fast the Universe is expanding? Many astronomers also believe it may also tell us the age of the Universe! The photographed "Cepheid variable" star in M100 brightens and dims over the course of days as its atmosphere expands and contracts. A longer blinking cycle means an intrinsically brighter star. Cepheid variable stars are therefore used as distance indicators. By noting exactly how long the blinking period is and exactly how bright the star appears to be, one can tell the distance to the star and hence the star's parent galaxy. This distance can then be used to match-up easily measured recessional velocity ("redshift") with distance. Once the "Hubble relation" was determined for M100, it can then apply to all galaxies - and hence can tell us how fast the Universe is expanding."

[zespaceblog]

RS Puppis and the Lady who Changed Astronomy Forever

RS Puppis is a curious star, but by no means alone in it's curiosity, in fact, it belongs to a group of stars known as Cepheid Variables.

The first variable star detected was (Eta) η Aquilae, followed a few months later by Delta Cephei, and it was the latter that gave it's name to a growing group of variable stars that were detected.

Since then, there have been many other kinds of variable stars found, for a variety of different reasons but it was Henrietta Leavitt that noticed a relationship between the Cepheid group, between the period of time they oscillated in brightness and the actual brightness.

So why does this matter ?

To steal a little journalistic explanation from the sourced site below, this knowledge helped know exactly how far away the famous Father Ted Cow was.

Just as Father Douglas couldn't understand why some cows are so tiny in the field and others so large, Astronomers had a problem, how can you say if a bright star is close by, or just massive ?

The genius of Leavitt was, in finding a relationship between the period of variability and the actual output of energy, we could compare Cepheid Variables no matter where they were, and later on, Edwin Hubble used this very fact to show Cepheid Variables in Galaxies were moving away from us, and in fact, pretty much all galaxies were moving away, leading to the proposition that they must have all come from an original source, the big bang.

Like far too many females in Astronomy, Leavitt was never recognised for her discovery at the time, but giving astronomy it's first standard candle, it led the way in proving galaxies were millions of light years away and not spiral nebula as they had previously been thought to have been.

Maybe if Cows shrank and grew in regular periods, this may have helped Father Douglas calculate the distance of the cows in the field, and saved Father Ted some prop based explanations.

Full credit for the anecdotes and topic of the day go to

Source :

Henrietta Leavitt and the Astronomical Cow Puzzle – The Wire Science

[lindahall]

Harlow Shapley – Scientist of the Day

Harlow Shapley, an American astronomer, was born Nov. 2, 1885.  

read more...

[livingforstars]

Andromeda Nebula: Var! - April 6th, 1996.

"In the 1920s, using photographic plates made with the Mt. Wilson Observatory's 100 inch telescope, Edwin Hubble determined the distance to the Andromeda Nebula - decisively demonstrating the existence of other galaxies far beyond the Milky Way. His notations are evident on the plate shown above (the image is a negative with stars appearing as black dots against the white background of space). By intercomparing plates, Hubble searched for "novae", stars which underwent a sudden increase in brightness. He found several on this plate and marked them with an "N". Later he discovered that one was actually a type of variable star known as a cepheid - crossing out the "N" he wrote "Var!" (upper right). Thanks to the work of Harvard astronomer Henrietta Leavitt, cepheids, regularly varying, pulsating stars, could be used as "standard candle" distance indicators. Identifying such a star allowed Hubble to show that Andromeda was not a small cluster of stars and gas within our own galaxy, but a large galaxy in its own right at a substantial distance from the Milky Way. Hubble's discovery is responsible for our modern concept of a Universe filled with galaxies."

[zespaceblog]

Hubble and the Expanding Universe

Until the James Webb Space Telescope begins active duty in the coming months, Hubble is still this blog's go-to place for our near galactic neighbourhood's most beautiful and diverse images. In many ways, these images are what we'll mark this era in our lives with, but Hubble isn't just about taking pretty pictures, there's serious science behind every single one of them.

Named after Edwin Hubble, an American astronomer who first proved that those spiral nebula's catalogued from 100's of years prior, were in fact galaxies, but more so, they were all (mostly) moving away from us, leading to the idea of a big bang and the expansion of the universe.

Fast forward 100 years, and the space telescope named after him, has been taking images of galaxies, capturing supernova in the act and spotting Cepheid Variable stars across millions of light years.

If you're wanting to compare objects in space to get a judgement on their distance and speed, having something that always has the same brightness or alternates in a predictable way, is going to be a great help. Some supernova and variable type stars exhibit this, these objects are known as standard candles.

There are various objects that can be used this way, but Hubble has expanded our ability to detect Cepheid Variables, and catch Type 1a supernova in the act, and all that data has been used to better calculate the expansion of the universe.

Even so, not all the calculations match, particularly the difference between these standard candles and the cosmic microwave background, which still to this day is not resolved, and probably points to some new physics we're missing in our understanding of the universe.

And that's what makes Astronomy so much fun, there's still so much to understand, so much to learn and find out.

Now, we wait for James Webb to take centre stage, Hubble will continue it's work, and no doubt, will collaborate with the James Webb, expect to see JWST data combined with Hubble in the coming years, giving an even greater resolution and hopefully understanding of this unimaginably huge universe we all live in.

[astroquizzical]

How Are Astronomical Distances Measured?

"How is astronomical distance determined? Just cannot get my head around cepheid variables, parallax, etc. How is it possible to tell how far away something is when you cannot bounce a radar beam off the object and time its return?"

Well, you’re absolutely right that radar is an ideal way of measuring distances to objects; with radar you bounce a radio or microwave pulse off of the other object (a planet, for instance) and wait for it to come back. The Arecibo Observatory in Puerto Rico is one of the best observatories...

Read the full article at Forbes!

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[christinetheastrophysicist]

A Group of Cepheids May Belong to an Unknown Galaxy

Title: Clustered Cepheid Variables 90 kiloparsec from the Galactic Center

Authors: Sukanya Chakrabarti, Roberto Saito, Alice Quillen, Felipe Gran, Christopher Klein, Leo Blitz

The regions near the galactic plane, where the majority of the Milky Way lies, is obscured by so much dust that it becomes difficult to study. In order to minimize dust obscuration, a team of astronomers led by Rochester Institute of Technology’s Sukanya Chakrabarti used near-infrared data from the VISTA Variables of the Via Lactea (VVV) public survey to search for stars at low latitudes near the center of the galaxy. With this survey, the team has discovered four Cepheid variable stars located almost 300,000 lightyears away.

Cepheid variables are pulsating stars. This pulsating results from the periodic change in brightness due to the expansion and contraction of the star's surface. It was discovered that a relationship existed between the Cepheid's luminosity and its period, and that it could be used to determine distances, both galactic and extragalactic. As a result, Cepheids are a type of ‘standard candles.’

The team focused on searching for faint variable stars with magnitudes greater than 15 in the infrared K-band and with periods greater than three days. They examined the stars’ light curves and the uncertainties in their periods. With this information, the team determined that the stars are Type I Cepheids. Also known known as classical Cepheids, they are the most common subclass of Cepheids.

These Cepheids are clustered together in such a way that suggests they may be associated with a dwarf galaxy. Previous research predicted that our galaxy may have interacted with a smaller dwarf galaxy 300 million years ago. Even though no dwarf galaxy with evidence of this interaction has been found, it is possible that a dwarf galaxy containing the Cepheids may exist in a region not studied by the survey. The team believes that it is possible to determine the structure of this object with further observations.

Image: V838 Monocerotis, a red supergiant variable star in the constellation Monoceros. (Credit: NASA, ESA and H.E. Bond (STScI))

[thenewenlightenmentage]

A stellar discovery on the Milky Way's far side

Five remarkable stars on the other side of our galaxy promise new insight into the outer reaches of our home turf.

A single Hubble Space Telescope image can capture scores of distant galaxies, but the one galaxy we'll never see from the outside is our own. As a result, no one knows the Milky Way's exact size and shape. It took more than a century after the discovery of the first spiral in space before astronomers established that our galaxy is a spiral, too, and more years elapsed before they deduced that we inhabit a barred spiral — a type whose bright central region is elongated. Now, for the first time, observers have detected five stars on the far side of the galaxy that serve as outstanding yardsticks, a feat which will divulge secrets about the Milky Way's terra incognita. "It's a beautiful piece of classic astronomy," says Leo Blitz, an astronomer at the University of California, Berkeley, who was not involved in the discovery.

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