The Map of Triton

August 26, 2014

There is a cool video of Neptune’s moon Triton that NASA has put together using Voyager 2’s images:

io9 has a great article on how this was put together, plus a summary of what we know of Triton.

Sorting Out the Candidates

July 2, 2014

At this point, I have created rgb images for all the objects I want to check out in the field of view of interest. There were hundreds of objects, but that is why computer programming exists. So that they do all the hard work. Unfortunately, there are some things that machines aren’t that good at. So, as a human, my job is to look at these images and identify candidates. Brown dwarfs are dim in the visible and shiny in the infrared. So, my job is to look for dots that are like that. Take this picture, for example:


The bottom left one is from DSS Red, which was taken the earliest, around 1990 or so, the top left one is from 2MASS, which was taken around 2000, and the right ones are from WISE, taken around 2010. The top and bottom left only differ on how the colors are scaled in terms of brightness. The top left one is linear stretch, and the bottom left one is logarithmic stretch. As you can see, logarithmic stretch is very helpful because  with linear, the star on top is so bright that the other dots are comparatively almost nothing. With logarithmic stretch though, a star 10 times as bright can be treated as if it were only twice as bright, and 100 times as bright as if it were only three times as bright. This allows dim objects to pop out.

This one is of interest because you can observe proper motion here. Each one were taken around a decade apart, and as you can see, the dots have moved slightly. It suggests of an object relatively close. As to whether it is a brown dwarf, I am not sure, but I am keeping tabs on it just in case. It is something I am gonna have to discuss with the professor.

Making Stars More Visible

June 20, 2014

Before I begin, there is a previous post that I would like to comment on my previous post. Apparently what I did was not combine three images and create an RGB image based on them. What happened instead was I put WISE 1, J, and K on top of each other, so all you could see was WISE 1 on top. Bummer. In order to do that, I have to install Montage, otherwise the images won’t rescale and stuff to fit each other. Unfortunately, it looks like a Linux kind of thing. Oh well.

Moving on to greener pastures, I have been changing a value called vmin and vmax. It allows me to set up a scale of color or black to white that depends on how bright the pixel is. So, let’s use the grayscale here for simplicity. If the pixel is as bright as the vmax value, then that pixel is white. If it is as dim as the vmin value, that pixel is black. In between it is all shades of gray. So, what happens, say if you bring the value of vmax down? The dimmer objects become whiter because now the brightness is closer to the vmax boundary. See here:


As you can see above, the bright object is still white when you lower the vmax boundary, but the whiteness becomes wider, while the dimmer object becomes whiter because it is closer to the line. That way, you can make dim objects stand out. See here two pictures below, one before the change, and one after:

1-2MASS J00332386-1521309-wise1

1-2MASS J00332386-1521309test

As you can see, it is much clearer that there is actually a thing shining right in the middle of the circle. I made the brown dwarf stand out.


In Which I Achieve Something

June 16, 2014

I made a colored picture using J band of 2MASS (1.25 micrometer), K band of 2MASS (2.17 micrometer), and Wise 1 (3.4 micrometer). Basically, each band represents the different wavelengths in which the telescopes captured the images. So, I put them together using python and got:


Neat! I believe the faint dot in the middle is the brown dwarf here. Hopefully I got did it right.

Planets of the Day: Kapteyn System and Kepler 10c

June 6, 2014

So, there have been two exciting planetary discoveries last week:

a) Two planets have been discovered around Kapteyn star, which is around 13 light years away. Since planets form with the star at around the same time, and the star is around 11.5 billion years old, the planets are the oldest known. Kapteyn star itself is likely to be a star of another tiny galaxy absorbed into the Milky Way, the remnant of that galaxy being the globular cluster Omega Centauri. Both planets are super Earth, with Kapteyn b having the possibility of liquid water to exist. Link here and here.

b) The most massive terrestrial planet yet has been discovered, and it is dubbed a mega Earth. Kepler 10c is 17 times the mass of the Earth, which is basically around Neptune’s mass. The size, though, is 2.3 times the Earth. This means the object has the density of a rock, so we know it can’t be a gas giant planet like Neptune. It is indeed a new type of planet, since a rocky planet is not expected to be this massive. I love surprises like this! More here and here.

I Got Sent More Reading Materials

June 5, 2014

I don’t have anything particular to say about them. They are pretty much a technical summary of brown dwarfs found, classification of spectra, proper motion (angle speed in sky), and distance, which were found using the 2MASS survey and WISE telescope. You can read them here, here, and here, if you want to learn more about brown dwarfs. They are pretty technical, though.

Update: You know what? I was mulling things over, and turns out there are a few things I want to comment about. Firstly, there is a spectral classification cooler than the T type, called the Y type, which is characterized by absorption from ammonia. These brown dwarfs are cooler than 600 K. The articles above talk about some of those.

Secondly, the articles above have a large focus on high proper motion brown dwarfs. Higher proper motion implies that the object are more probable to be closer to us than those having low proper motion. Think about it this way, when you are in a car, things that are far away look slower than things that are closer to you. It’s not so much that in reality things that are farther away are slower, as it is the fact that things that are farther away has lesser angular movement because distances look smaller when farther away.

How are proper motion found? Well, turns out that the 2MASS survey took observations a decade previous to WISE telescope. So, you look at the pictures from 2MASS, and you look at one from WISE, and see how much the position has changed in angle. The objects are likely to have constant speed, so just divide the angle difference by the year difference.

What is proper motion helpful for? Well, it let us know that an object is likely to be close to the solar system. This is supposed to help bridge the gap in our knowledge of the solar system neighborhood. The distance itself can later be taken using parallax. Aside from that, finding close brown dwarfs is also helpful because it will help us study the atmosphere better. We still have an imperfect model on the process behind condensation and cloud formation in the brown dwarf atmosphere, and the more of them we find, the better we will know the details behind it.

Brown Dwarf Pics

June 3, 2014

This is what an image for brown dwarf looks like, just a faint dot. As you can see in the link, each of those four images represent the different wavelength of infrared the pictures were taken. Obviously WISE band 1 and 2 (WISE is the name of the telescope) are best for this sort of stuff. Oh, and fun fact, this one was discovered by my prof.


Introduction to my Research: Brown Dwarfs

June 2, 2014

So, I got accepted into a summer research program. They are going to pay me and everything, yay! Which is why I thought I should blog about my research.

What I am doing this summer is basically sift through infrared data and looking for object called brown dwarfs and classifying them. Brown dwarfs are in a way objects that represent the transitions between planets and stars. They are much more massive than planets, enough to have fused deuterium (hydrogen, but with a neutron) for a short while, but they are not massive enough to fuse regular hydrogen. The mass may range from 13 to 80 Jupiters. After the short lived deuterium fusion phase, they just start cooling down. They tend to emit most of the light in the near infrared zone. Size wise, they are not too different from Jupiter because the interior pressure is governed by electron degeneracy. Basically, the pressure of electrons due to them not being able to occupy the same energy states is what holds the object from further collapse. In a pressure dominated by degenerate matter, adding more mass doesn’t cause an object to grow much.

How does one empirically distinguish a brown dwarf from a low mass star? There is a simple test called the Lithium test. If one can detect lithium, it is probably a brown dwarf. Stars are hot enough to be able to fuse lithium, unlike brown dwarfs, and lithium fuses at a similar temperature to hydrogen. That said, the highest mass brown dwarfs can burn lithium, so at the high end range of brown dwarf mass, they are indistinguishable from stars. Well, there is another way, but it is harder to do. Basically, measure the temperature and mass of a brown dwarf binary. The theory is that an object of certain mass will have a different temperature curve as it ages than one of a different mass. If an object is massive enough to be a star, the temperature will stabilize due to sustained fusion, if not it keeps cooling down.

Before we go on, I would like to address how we can know what compounds such a distant object have. We look at the spectrum of light from the object, and see which wavelengths are missing. Certain compounds absorbs light at certain specific frequencies because of the way the electrons are configurated energy wise. Electrons can only occupy certain energies, and so they will absorb only light of certain energies.  So, when you look at the spectrum of light coming off the planet, there will be chunks of light that will be missing corresponding to the energy absorbed. Imagine that the rainbow has various thin strips on it missing, that is what it is like.

Brown dwarfs come in two spectral type, the L type and the T type, with L being the hotter, more luminous type. The temperature itself is correlated with luminosity by the fourth power, so measuring luminosity gives you the temperature. The spectral types are related to what compounds one detects in the atmosphere. The L types have the temperature range of 1300 K to 2500 K. The hottest L type show vanadium oxide and titanium oxide absorption signatures in the spectra, and as the brown dwarf gets cooler, this transitions to a spectra with absorption due to metal hydride (FeH, MgH, CaH, etc) and Alkali metal compounds (NaI, KI, etc), while the metal oxide absorption disappears. The T type are objects below 1500 K, and the spectra contains absorptions from methane, water, ammonia, and CO. Does this mean that the transition of  spectra represents another good way to gauge the temperature of the object? Yes for early L and late T. Not so much for the transition between late L to early T. In that section, the temperature doesn’t change very much while the spectra changes. A point of note is that the temperature/spectra correlation works much better with optical than infrared.

There is a reasonable explanation for the transitions of spectra a brown dwarf undergoes. As the brown dwarf cools, the metal oxides condense and fall off deeper into the atmosphere. This uncovers the spectra from the alkali metals and hydride metals. As the temperature goes lower to the T type level, clouds become an important component. This explains the rapid change in spectra with the slower change in temperature as this transition of dusty atmosphere occurs around a short range around 1400 K.  At temperatures lower than 1400 K, the dust sinks and the metal hydrides condense while conditions are right for the reaction of CO+H2=H2O+CH4 occurs, meaning carbon monoxide with hydrogen reacts to for water and methane. This explains the methane absorption that dominates in the T brown dwarfs.

Finally, I would like to point out the model pointed out above for the brown dwarfs differs with metallicity. Metals in astronomy are all elements with higher atomic number than helium. Brown dwarfs are allowed to be more massive and hotter with less metal.

This is a basic summary of what we know about brown dwarfs. If you want to know more about them, you can of course go ahead and read what I linked below. There has also been some advances, like the discovery of below freezing brown dwarfs. And there are mysteries to be solved, like the fact that there are three scenarios for condensations and dusts that plays a key role in the late L to early T spectrum.

I have done all this preliminary reading. Hopefully I know what I will be doing. Granted, there will be some fumbling around as this is my first legit science project ever.

Source and reading materials,2001.html (brown dwarf)

A Little Something on Triton

May 28, 2014

Here is a video on Neptune’s largest moon Triton, with a cute Triton thumbnail. It is a great summary of the basic facts regarding this object:

Star Endings: Pair Instability and Photodisintegration

May 27, 2014

Population III Stars

For the third part in the series of posts on star deaths, we look at deaths at the most extreme ends. They happen to enormously massive stars that were only common during the beginning of the universe, called the population III stars. Population III stars are a class of hypothetical first generation, never observed stars, that are believed to be over a hundred times more massive than the sun, and have none or almost no metal ( in astronomy any element of higher atomic number than helium).  Now, why they are called population III instead of I, don’t ask me, but turns out it is all reversed. Population II is the metal poor stars, and population I is metal rich stars like the sun.

While stars of 100+ solar mass exists in today’s universe (as seen here), they are extremely rare. In terms of probability, there is the fact that this kind of massive stars are extremely short lived compared to other stars, less than 10 million years compared to billions of years like the sun. In terms of the time scale of the universe, that is a blink of an eye, so more likely than not, you will miss it. Physically, huge stars form more easily in metal poor condition. The presence of metals allow for further cooling of gas to takes place, which inhibits the formation of huge stars. The temperature is important because the hotter the gas, the higher the gas pressure is, which counteracts the force of gravity. So, cooler gas contracts further, which gets fragmented in the process, creating smaller stars. In that way, metallicity is once again shown to be a powerful factor in determining the life and times of a star.

So, considering the hypothetical/theoretical nature of these objects and events, should we take all of this with a grain of salt? Well, yes and no. We do believe the theories are correct because they have worked in other situations. At the same time, that doesn’t mean we know all the details, and those details do matter when formulating accurate theories. Furthermore, there are the issues of rotation. The way I think of it is, the general picture is likely to be right, but if new observations come that contradict certain aspects of the models, then of course, I change my mind. That said, these are issues that are already being probed, with the search of population III stars being a high priority, and hey look, pair instability supernovas are already looking very likely.

Pair Instability End

Pair instability happens to stars beyond 140 solar mass. The energy in the core is such that the photons in there create electron-positron pairs. This happens because other forms of energy can be transformed into matter, and due to conservation principles, of charge (+1 for positive charge, -1 for negative charge) and particle number(+1 for matter, -1 for antimatter). Enough energy is taken away in the process that gravity dominates and the core starts contracting. Now, pair instability does occur in lower mass stars, around 100 to 140 solar masses, but it isn’t  enough to cause a runaway nuclear explosion. Instead, it will increase nuclear reaction until gravity and pressure balances out. This pulsation goes on until a star loses enough mass so pair instability doesn’t happen. Otherwise, the collapse of the core causes an uncontrollable reaction of oxygen and silicon to begin. While turning a huge amount of mass into Nickel 56, the core bounces back from collapse. What ends up happening is an extremely energetic explosion that leaves no remnant of the star behind. The star has pretty much been completely obliterated. Well, I guess you count count the gas and dust left by the star as remnant if you want…

Photodisintegration End

At the 250 solar mass point, a star dies by photodisintegration instability. At the energy generated by this star, a significant portion of the photons gets used up splitting atoms apart. The core collapses without the energy needed to hold up the star from its own gravity, and a black hole forms. This is pretty much core collapse, as in previous post, but with a different reason for the instability to happen, so some of the detail from the previous post about degeneracy and black holes applies here. I am not exactly sure at which part of the chain of nuclear reactions this happens at, though.

I wish I could say that there have been this kind of supernova observed. As far as I can see, I haven’t found any article regarding any observation of this type of supernova. So, for now you can put this entirely in the hypothetical area in your mind.


With this, I conclude the three series of posts on how stars die. Now you know the general process of how stars die, with some of the gory details displayed. If they felt dense, I feel for you. Even I learned a lot on the nuances of these processes, and had one hell of a time researching a lot of these facts. Even so, if these posts have informed you and made you interested in astronomy, well then I am happy. If it made you want to vomit, I am okay with that too, just tell me what went wrong!

Sources and Reading Materials

Click to access Bromm02.pdf

Click to access 0107037v2.pdf

Click to access 0905.0929v1.pdf

Click to access 52134.web.pdf

Click to access 0212469v1.pdf