Lacerta
Posted: Thu Sep 29, 2011 1:19 pm
http://en.wikipedia.org/wiki/Lacerta wrote: <<Lacerta is one of the 88 modern constellations defined by the International Astronomical Union. Its name is Latin for lizard. A small, faint constellation, it was created in 1687 by the astronomer Johannes Hevelius. Its brightest stars form a "W" shape similar to that of Cassiopeia, and it is thus sometimes referred to as 'Little Cassiopeia'. It is located between Cygnus, Cassiopeia and Andromeda on the northern celestial sphere. The northern part lies on the Milky Way.
Centred on a region of the sky without apparently bright stars, Lacerta was not regarded as a constellation by ancient astronomers. Before Johannes Hevelius'es creation of the constellation, this area, including the "rock of" Andromeda, was assembled by Royer to form the constellation Sceptrum et Manus Iustitiae. Later, when Lacerta sive Stellio was established, Bode created the constellation Frederici Honores for the dropped "rock of" Andromeda part. Both Sceptrum et Manus Iustitiae and Frederici Honores are now obsolete and not used by astronomers, while Lacerta still survives.
Coincidentally, the Chumash people of California call this part of the sky 'Lizard' and include it in multiple stories.
Lacerta is typical of Milky Way constellations: no bright galaxies, nor globular clusters, but instead open clusters, for example NGC 7243, the faint planetary nebula IC 5271 and quite a few double stars. It also contains the prototypic blazar BL Lacertae. Lacerta contains no Messier objects.
Stars:Deep sky objects:
- α Lac: this main sequence star of spectral type A1 V has an apparent magnitude of merely 3.77; Lacerta has no other stars brighter than fourth magnitude. α Lac is an optical double star.
Roe 47: a multiple star consisting of five components (magnitudes 5.8, 9.8, 10.1, 9.4, 9.8).
ADS 16402 is a binary star system in Lacerta, around which a planet orbits with some unusual properties.[1] The Jupiter-sized planet exhibits an unexpectedly low density, about the same as cork. This planet is dubbed HAT P-1.
- NGC 7243: an open star cluster of approximately 6.4m.
BL Lacertae: it was discovered quite early and first thought to be a star and therefore given a variable star designation. However, in reality it is the core of a galaxy. It lent its name to a whole type of celestial objects, the BL Lacertae objects (a subtype of blazar.) The object varies irregularly between magnitudes 14 and 17 over a few days.>>
harry wrote:G'day
The Mouse That Roared: Pipsqueak Star Unleashes Monster Flare
http://www.nasa.gov/centers/goddard/new ... _star.html
On April 25, NASA’s Swift satellite picked up the brightest flare ever seen from a normal star other than our Sun. The flare, an explosive release of energy from a star, packed the power of thousands of solar flares. It would have been visible to the naked eye if the star had been easily observable in the night sky at the time.
The star, known as EV Lacertae, isn’t much to write home about. It’s a run-of-the-mill red dwarf, by far the most common type of star in the universe. It shines with only one percent of the Sun’s light, and contains only a third of the Sun’s mass. At a distance of only 16 light-years, EV Lacertae is one of our closest stellar neighbors. But with its feeble light output, its faint magnitude-10 glow is far below naked-eye visibility.
"Here’s a small, cool star that shot off a monster flare. This star has a record of producing flares, but this one takes the cake," says Rachel Osten, a Hubble Fellow at the University of Maryland, College Park and NASA’s Goddard Space Flight Center in Greenbelt, Md. "Flares like this would deplete the atmospheres of life-bearing planets, sterilizing their surfaces."
http://en.wikipedia.org/wiki/EV_Lacertae wrote: EV Lacertae (EV Lac, Gliese 873, HIP 112460) is a faint red dwarf star 16.5 light years away in the constellation Lacerta. It is the nearest star to the Sun in that region of the sky, although with an apparent magnitude of 10, it is only barely visible with binoculars. EV Lacertae is spectral type M3.5 flare star that emits X-rays.
On 25 April 2008, NASA's Swift satellite picked up a record-setting flare from EV Lacertae. This flare was thousands of times more powerful than the largest observed solar flare. Because EV Lacertae is much farther from Earth than the Sun, the flare did not appear as bright as a solar flare. The flare would have been visible to the naked eye if the star had been in an observable part of the night sky at the time. It was the brightest flare ever seen from a star other than the Sun.
EV Lacertae is much younger than our Sun, and still spinning rapidly. The fast spin, together with its convective interior, produces a magnetic field that is much more powerful than the Sun's. This strong magnetic field is believed to play a role in the star's ability to produce such bright flares.
Its location in the sky is at RA 22h 46m 49.7s, DEC +44° 20′ 02″.>>
http://en.wikipedia.org/wiki/BL_Lacertae wrote:
<<BL Lacertae or BL Lac is a highly variable, extragalactic AGN (active galactic nucleus or active galaxy). It was first discovered by Cuno Hoffmeister in 1929, but was originally thought to be an irregular variable star in the Milky Way galaxy and so was given a variable star designation. In 1968, the "star" was identified by John Schmitt at the David Dunlap Observatory as a bright, variable radio source. A faint trace of a host galaxy was also found. In 1974, Oke and Gunn measured the redshift of BL Lacertae as z = 0.07, corresponding to a recession velocity of 21,000 km/s with respect to the Milky Way.
BL Lacertae is the original member of a type of blazar known as "BL Lacertae objects"; also termed simply "BL Lac objects". This class is distinguished by optical spectra devoid of the broad emission lines characteristic of quasars. On occasion, however, BL Lacertae has been observed to display weak emission lines.
BL Lacertae changes in apparent magnitude over fairly small time periods between values of 14 and 17.
Its location in the sky is at RA 22h 02m 43.3s, DEC +42° 16′ 40″.>>
http://www.nytimes.com/2006/09/15/science/space/15planet.html?ref=spaceandcosmos wrote:
Puzzling Puffy Planet, Less Dense Than Cork, Is Discovered
By KENNETH CHANG
Published: September 15, 2006
Strange New Planet Discovered
A planet around a distant star appears inexplicably puffy, astronomers reported yesterday. The planet is wider than Jupiter. But with half the mass, it is less dense than cork. In a cosmic bathtub, it would float. The astronomers said they were baffled about how the planet formed and how it remained so puffy. “The short answer is, I have no idea,” said Dimitar Sasselov, a professor of astronomy at Harvard and a member of the research team. “It’s a very strange planet.”
The planet, designated HAT-P-1b, was found orbiting a star 450 light-years away in the constellation Lacerta. It is the second of its kind that has been located. The first was found circling the star HD 209458 in 1999. At that time, astronomers speculated that perhaps an unusual event — for example, that the star had somehow been knocked on its side, generating tidal forces that heat the interior — led to its puffiness. With the discovery of a second low-density planet, astronomers are wondering whether they are flukes or there is a whole class of puffy planets in the universe formed by a common process not yet understood. “Now we have two of them, and we wonder if we should go back to the drawing board,” said Robert W. Noyes, a senior astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and another member of the research team. The findings have been submitted to The Astrophysical Journal and were announced at a news conference at the Smithsonian Institution.
An automated network of telescopes noticed that in the double-star system ADS 16402 in Lacerta, one star dimmed about 1.5 percent for two hours every four and a half days. The data suggested that something was periodically passing in front of it and blocking some light. The astronomers took a closer look with larger telescopes. They were also able to verify the presence of HAT-P-1b by detecting four-and-a-half-day wobbles in the frequency of the star’s light caused by the gravitational pull of the planet.
Many planets detected around other stars have been “hot Jupiters,” gas giants like Jupiter or larger, in very close orbits around the stars. The new planet falls into that category, circling at a distance one-twentieth that between Earth and the Sun. While gas giants like Jupiter and Saturn are primarily hydrogen and helium, they also possess rocky cores and crushing pressures within that squeeze the hydrogen and helium to higher densities. Jupiter’s average density is 133 percent as dense as water. Saturn’s is 70 percent that of water. The density of HAT-P-1b is one-quarter that of water. “Both Saturn and this planet would float on water, but this one would float a lot higher,” Dr. Noyes said. “The low densities would suggest very few rocks at the core.”
Astrophysicists now have two problems to solve: how a planet that has almost no elements heavier than hydrogen and helium can form and how it stays hot. “Our lack of understanding is worse than we thought it was,” said Alan P. Boss, a planetary theorist at the Carnegie Institution of Washington who was not involved in the research.
Almost certainly, higher-than-expected temperatures within HAT-P-1b cause the gases to expand and the planet to puff. Its diameter, 38 percent wider than Jupiter, is 24 percent bigger than theories predicted. HAT-P-1b’s proximity to the star is insufficient explanation. Gas giants actually do pass through a puffy period in their youth when they are much hotter and then contract as they cool. Neither star, however, is young, and neither planet is likely to have formed recently.
“From the point of view of planetary theory, they’re in a region we would call Neverland,” Dr. Sasselov said. Like Peter Pan, the two planets seem to have found a way to maintain their youthful appearance. One idea that Dr. Sasselov is exploring is that hydrogen and helium separate in a puffy planet, forming layers like oil on water. The energy from the heavier helium’s falling to the center of the planet might be enough to explain the heating, he said. “That’s an exotic scenario,” Dr. Sasselov said. “It’s a possibility.”
Another possibility is that a second planet is pulling HAT-P-1b into an eccentric orbit that would heat the interior through friction caused by the tides. That cannot be the case for the HD 209458 planet, however, because years of observations have shown the orbit to be almost circular. Dr. Sasselov said he thought it unlikely that the two large planets had been slammed in a way that tipped them on their sides, adding, “It’s like an impossible billiards ball hit.”>>
http://en.wikipedia.org/wiki/HAT-P-1b wrote:
<<HAT-P-1b is an extrasolar planet orbiting the Sunlike star HAT-P-1, also known as ADS 16402 B. HAT-P-1 is the dimmer component of the ADS 16402 binary star system. It is located 453 light years away from Earth in the constellation Lacerta. HAT-P-1b is among the least dense of any of the known extrasolar planets.
HAT-P-1b was detected by searching for astronomical transits of the parent star by orbiting planets. As the planet passes in front of its parent star (as seen from Earth), it blocks a small amount of the light reaching us from the star. HAT-P-1b was first detected by a dip of 0.6% in the light from the star. This enabled determination of the planet's radius and orbital period. The discovery was made by the HATNet Project (Hungarian Automated Telescope Network) using telescopes in Arizona and Hawaii and announced on September 14, 2006.
HAT-P-1b is located in a very close orbit to its star, taking only 4.47 days to complete. It therefore falls into the category of hot Jupiters. At only 8.27 million kilometers from the star, tidal forces would circularise the orbit unless another perturbing body exists in the system. At the present time, the existing measurements are not sufficient to determine the orbital eccentricity, so a perfectly circular orbit has been assumed by the discoverers. However, the eccentricity of the planet was calculated to be no greater than 0.067.
In order to determine the mass of the planet, measurements of the star's radial velocity variations were made by the N2K Consortium. This was done by observing the Doppler shift in the star's spectrum. Combined with the known inclination of the orbit as determined by the transit observations, this revealed the mass of the planet to be 0.53±0.04 times that of Jupiter.
As evidenced by its high mass and planetary radius, HAT-P-1b is a gas giant, most likely composed primarily of hydrogen and helium. The planet would thus have no well-defined surface. Current theories predict that such planets formed in the outer regions of their solar systems and migrated inwards to their present orbits.
HAT-P-1b is significantly larger than predicted by theoretical models. This may indicate the presence of an additional source of heat within the planet. One possible candidate is tidal heating from an eccentric orbit, a possibility which has not been ruled out from the available measurements. However, another planet with a significantly inflated radius, HD 209458 b, is in a circular orbit.
An alternative possibility is that the planet has a high axial tilt, like Uranus in our solar system. The problem with this explanation is that it is thought to be quite difficult to get a planet into this configuration, so having two such planets among the set of known transiting planets is problematic.
Its location in the sky is at RA 22h 57m 47ss, DEC +38° 40′ 30″.>>
