# Stars/Oranges

The variability of BD +50 961 (SY Persei, an orange star) is confirmed.
"ESO Photo Ambassador Babak Tafreshi snapped this remarkable image [at left] of the antennas of the Atacama Large Millimeter/submillimeter Array (ALMA), set against the splendour of the Milky Way. The richness of the sky in this picture attests to the unsurpassed conditions for astronomy on the 5000-metre-high Chajnantor plateau in Chile’s Atacama region."
"This view shows the constellations of Carina (The Keel) and Vela (The Sails). The dark, wispy dust clouds of the Milky Way streak from middle top left to middle bottom right. The bright orange star in the upper left is Suhail in Vela, while the similarly orange star in the upper middle is Avior, in Carina. Of the three bright blue stars that form an “L” near these stars, the left two belong to Vela, and the right one to Carina. And exactly in the centre of the image below these stars gleams the pink glow of the Carina Nebula"

## Orange supergiants

In the photograph at right, the orange super giant star Betelgeuse is shown in relationship with the dense nebulas of the Orion Molecular Cloud Complex and Orion's Belt.
Eta Pavonis on the lower right is an example of a super giant orange star. It is specifically spectral type K2II according to SIMBAD.

## Orange giants

Arcturus (α Boötis) is an orange (K1.5III) giant per SIMBAD.
According to SIMBAD HD 152334, or Zeta$^2$ Scorpii is a spectral type K4III star. In the image at right, it is the orange star on the left. It is a single star. Its actual color has less red in it as does that of zeta1 Scorpii, the blue giant on the right. The image on SIMBAD by AladinLite is from DSS2. It has the correct colors.

## Brown dwarfs

Brown dwarfs are sub-stellar objects that have fully convective surfaces and interiors, with no chemical differentiation by depth. Brown dwarfs occupy the mass range between that of large gas giant planets and the lowest-mass stars; this upper limit is between 75$^{[1]}$ and 80 Jupiter masses ($M_{J}$).
Astronomers have reported that spectral class T brown dwarves (the ones with the coolest temperatures) are colored magenta because of absorption by sodium and potassium atoms of light in the green portion of the spectrum.
"The star on the left is so much brighter than the "coolest star" that it creates the white streak and dramatic pattern visible in the image."

### 2MASS J10475385+2124234

"2MASS J10475385+2124234 [is] a brown dwarf more than 33 light-years away in the constellation Leo. The dwarf ... has a surface temperature of just ... 900 Kelvin ... Jupiter's lights are linked to its rapid rotation ... Since brown dwarfs are comparable in size to Jupiter, the brown dwarf flare mechanisms might arise similarly. ... [When] first examined using the ... fixed radio dish at Arecibo Observatory in Puerto Rico In several observations, ... flares of radio activity [occurred] ... [Using the] Karl G. Jansky Very Large Array (VLA) of telescopes ... The radio waves emanating ... are about 4.5 times fainter than the previous record ... observing ... LPP 944-20."

## Sub-brown dwarfs

A sub-brown dwarf is an astronomical object of planetary mass that is not orbiting a star and is not considered to be a brown dwarf because its mass is below the limiting mass of about 13 Jupiter masses). Sub-brown dwarfs are formed in the manner of stars, through the collapse of a gas cloud (perhaps with the help of photo-erosion), and not through accretion or core collapse from a circumstellar disc Johnstonalthough not universally agreed upon; astronomers are divided into two camps as whether to consider the formation process of a planet as part of its division in classification. The smallest mass of gas cloud that could collapse to form a sub-brown dwarf is about 1 M$_J$. This is because to collapse by gravitational contraction requires radiating away energy as heat and this is limited by the opacity of the gas.

## Novas

On September 3, 1885, the Nova Andromedae exhibited "Colour orange. Nebula around Nova very ruddy." On September 5, 1885, the same nova appeared, "Very light, but not bright orange. Nebula ruddy." By the 6th, it was "Dull orange."
In the image at right, the orange filaments are the tattered remains of the star and consist mostly of hydrogen.

## Star-forming regions

"Looking like an elegant abstract art piece painted by talented hands, this picture is actually a NASA/ESA Hubble Space Telescope image of a small section of the Carina Nebula. Part of this huge nebula was documented in the well-known Mystic Mountain picture (heic1007a) and this picture takes an even closer look at another piece of this bizarre astronomical landscape (heic0707a)."
"The Carina Nebula itself is a star-forming region about 7500 light-years from Earth in the southern constellation of Carina (The Keel: part of Jason’s ship the Argo). Infant stars blaze with a ferocity so severe that the radiation emitted carves away at the surrounding gas, sculpting it into strange structures. The dust clumps towards the upper right of the image, looking like ink dropped into milk, were formed in this way. It has been suggested that they are cocoons for newly forming stars."
"The Carina Nebula is mostly made from hydrogen, but there are other elements present, such as oxygen and sulphur. This provides evidence that the nebula is at least partly formed from the remnants of earlier generations of stars where most elements heavier than helium were synthesised."
"The brightest stars in the image are not actually part of the Carina Nebula. They are much closer to us, essentially being the foreground to the Carina Nebula’s background."
"This picture was created from images taken with Hubble’s Wide Field Planetary Camera 2. Images through a blue filter (F450W) were coloured blue and images through a yellow/orange filter (F606W) were coloured red. The field of view is 2.4 by 1.3 arcminutes."

## Globular clusters

"The dazzling stars in Messier 15 [at right] look fresh and new in this image from the NASA/Hubble Space Telescope, but they are actually all roughly 13 billion years old, making them some of the most ancient objects in the Universe. Unlike another recent Hubble Picture of the Week, which featured the unusually sparse cluster Palomar 1, Messier 15 is rich and bright despite its age."
"Messier 15 is a globular cluster — a spherical conglomeration of old stars that formed together from the same cloud of gas, found in the outer reaches of the Milky Way in a region known as the halo and orbiting the Galactic Centre. This globular lies about 35 000 light-years from the Earth, in the constellation of Pegasus (The Flying Horse)."
"Messier 15 is one of the densest globulars known, with the vast majority of the cluster’s mass concentrated in the core. Astronomers think that particularly dense globulars, like this one, underwent a process called core collapse, in which gravitational interactions between stars led to many members of the cluster migrating towards the centre."
"Messier 15 is also the first globular cluster known to harbour a planetary nebula, and it is still one of only four globulars known to do so. The planetary nebula, called Pease 1, can be seen in this image as a small blue blob to the lower left of the globular’s core."
"This picture was put together from images taken with the Wide Field Channel of Hubble's Advanced Camera for Surveys. Images through yellow/orange (F606W, coloured blue) and near-infrared (F814W, coloured red) filters were combined. The total exposure times were 535 s and 615 s respectively and the field of view is 3.4 arcminutes across."
"This bright spray of stars [at second right] in the small but evocative constellation of Delphinus (the Dolphin) is the globular cluster NGC 6934. Globular clusters are large balls of (typically) a few hundred thousand ancient stars that exist on the edges of galaxies."
"Lying 50 000 light-years from Earth, in the outer reaches of our Milky Way galaxy, NGC 6934 is home to some of the most distant stars still to be part of our galactic system — in a sense, it is a far-flung suburb to the Milky Way’s city centre."
"NGC 6934 was first seen by William Herschel in the late eighteenth century. He classified it as a “bright nebula” and was not able to resolve it into stars. The cluster is not bright enough to see with the naked eye, and even in ideal conditions it is very difficult to view with binoculars. However, it is a popular target for amateur astronomers as it can easily be observed using relatively inexpensive telescopes. Broadcaster Patrick Moore, presenter of BBC TV’s The Sky at Night for more than 50 years, included this cluster in his “Caldwell catalogue” of celestial objects that amateur astronomers should look out for."
"NGC 6934’s faintness is down to its distance — not how bright it really is. With its many thousands of stars, the cluster is no minnow. The fact that the huge core of our galaxy dwarfs it, along with the other 150 or so globular clusters that orbit the Milky Way’s galactic centre, is a reminder of the breathtaking scale of the cosmos."
"This picture was taken with the Wide Field Channel of the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys. It was created from images taken through filters F814W (near infrared) and F606W (orange), coloured red and blue respectively. The exposure times were 29 minutes per filter, and the field of view is 3.3 arcminutes across."

## Gaseous objects

"Stars come in all different colors. The color of a star indicates its surface temperature, an important property used to assign each star a spectral type. Most stars in the above Sagittarius Star Cloud are orange or red and relatively faint, as our Sun would appear. The blue and greenish stars are hotter, many being relatively young and massive. The bright red stars are cool Red Giants, bloated stars once similar to our Sun that have entered a more advanced stage of evolution. Stars of this Sagittarius Cloud lie towards the center of our Galaxy - tantalizing cosmic jewels viewed through a rift in the dark, pervasive, interstellar dust. This famous stellar grouping houses some of the oldest stars known."