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  • tnithyanandan 7:08 pm on March 21, 2014 Permalink | Reply
    Tags: , Cosmology, , , low frequency, , power spectra, radio, , ,   

    Joining ASU and a peek into my research 

    My name is Nithyanandan Thyagarajan. I joined the LoCo (Low frequency Cosmology) lab group at ASU SESE headed by Prof. Judd Bowman, in September 2013 as a postdoctoral research scholar. I did my bachelor’s in Electrical Engineering from IIT Madras, India. For my PhD thesis at Columbia University, I worked on identifying and characterizing variable and transient radio objects by conducting one of the biggest searches of its kind in the radio sky. I then moved to Raman Research Institute in Bangalore, India as a postdoc and worked on statistical characterization of foreground contamination in the power spectrum of redshifted 21 cm line emission of neutral hydrogen during the epoch of reionization (EoR). During this period I got associated with the Murchison Widefield Array (MWA) project.

    The LoCo group has members involved in a variety of interesting projects. Besides having a strong presence in the MWA project, the members are also involved in other EoR experiments using the Experiment to Detect the Global EoR Step (EDGES), Precision Array for Probing the Epoch of Reionization (PAPER), Dark Ages Radio Explorer (DARE), Long Wavelength Array (LWA) and other theoretical and modeling projects. I am excited to be a part of this diverse group which provides enormous opportunities to learn science through the many perspectives from these different experiments.

    Currently, I am focusing on setting up simulations to predict the response of the MWA telescopes to all-sky radio emission. My aim is to isolate and characterize the signatures of different spatial structures of foreground objects such as the Milky Way, and other extragalactic objects besides the instrument’s own systematic effects on the observed power spectrum that contains information about the spatial distribution of redshifted 21 cm line emission from neutral hydrogen from the EoR. An understanding of the radio foreground objects and that of the telescope is extremely significant because the expected signatures from the neutral hydrogen emission during the EoR are extremely faint compared to the contamination from radio foregrounds and instrumental artifacts. Detecting EoR signal may be impossible without a precise removal of such contamination and artifacts.

    Here’s an approximate simulation of the radio foreground and instrumental signatures we expect to see in the power spectrum when the entire hemisphere of the sky is observed by the MWA telescope. The simulations are found to match well with results from analysis of data from the MWA telescopes.

    Predicted spatial power spectra of a an all-sky model as seen by MWA telescopes.

    Predicted spatial power spectra of an all-sky radio model of foreground objects as seen by MWA telescopes. The all-sky radio emission model is shown in the central panel. The peripheral panels show the power spectra recorded by different antenna pairs (x-axis) grouped by orientation of the lines joining them (EW at bottom right, NE at top right, NS at top center, and NW at top left). The x-axes in all the peripheral panels represent the different antenna pairs which sample the transverse spatial information from emission from the plane of the sky while the y-axes sample spatial structures into the plane of the sky. Since the sky model contains heterogeneous spatial structures, these different antenna pairs record different spatial information. The wedge/fork shaped feature prominent in the top center panel and the bright horizontal feature in all the peripheral panels arise out of the emission from our galaxy and other extragalactic radio emission (all the bright features enclosed by the forked black lines). The periodically repeated horizontal structures are caused by the frequency characteristics of the MWA telescopes.

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  • dannyjacobs 3:08 pm on April 10, 2013 Permalink | Reply
    Tags: , , , radio   

    In the name of science 

    Science experiments, as in life, are plagued by uncertainties.  As sarah showed last week, a particularly pernicious one is the response of the  telescope across the image. Things tend to get dimmer towards the edges, but without some very well known source in that area, its difficult to correct.  Most telescopes get around this problem by physically scanning across a known source, tracing out the response function.  Our new low frequency telescopes (MWA,PAPER) are fixed to the ground, we do not have the option of moving the telescope. So its time to get creative.  We can use satellites, known astronomical radio sources, or we can even fly a known transmitter over the telescope.

    So, I hope this explains this picture here.

    IMG_1500

    Danny flying the Octocopter. Next, we’ll be attaching a calibration antenna.

    The Octocopter is on loan from our colleagues at Curtin University. (Here’s a great video they made with it.) We’ll be attaching a calibration source and flying grid pattern over the telescope.  Today we just attached a go pro camera.  Here’s the footage

     
  • seasterb 2:23 pm on March 25, 2013 Permalink | Reply
    Tags: , , , radio   

    Is it Abstract Art or Science? 

    Many cosmological questions about the early universe are on the horizon of scientific discovery at this time. Theorists have come up with a time line that shows the development from the Big Bang to the present gigantic and complex universe. Can we prove what the theorists have predicted? Perhaps – but with every measurement there is some amount of error and uncertainty. Unfortunately, the uncertainty that can be tolerated in our group’s experiments to be able to state definitively, “We know when the first stars and black holes formed” is ridiculously small. The project that I have been working on for the last year set out to find the error related with using an antenna at varying locations on the Earth and different times during the day to make accurate measurement of the radio spectrum. Every antenna has a beam pattern – which is the area that an antenna can collect information from, and each beam pattern has places that are more sensitive and less sensitive to incoming signals.
    By projecting these beam patterns onto a temperature coded map of the sky, an estimate of what that antenna can “see” at that time, frequency, and location on the globe can be made – but if you ask me, most of the information I get resembles a painting I would love to hang on my wall.

    Figure 1- Sky Map at 408 MHz

    Figure 1- Sky Map at 408 MHz


    Figure 2-Beam in Azimuth and Elevation

    Figure 2-Beam in Azimuth and Elevation


    Figure 3 - Beam in Right Ascension and Declination

    Figure 3 – Beam in Right Ascension and Declination


    Figure 4 - Beam Projected on the Sky Map

    Figure 4 – Beam Projected on the Sky Map

    Figure 1 shows the temperature coded map of radio emission from our own Milky Galaxy in the sky – red is hot and blue is cold. Figures 2 and 3 above show how the modeled beam pattern looks for a physical antenna in two different astronomical coordinate systems. Figure 4 filters the beam pattern, modeled on the data set generated for the antenna beam pattern filtered by RA/DEC, against the sky map. On the color scale, red is the strongest signal and blue is the weakest signal. So as the earth rotates, the sky over the antenna will change and the red, or strongest collecting point, will hit different parts of the sky. In Figure 4, the beam pattern was projected on the galactic sky map at an arbitrary latitude, longitude, and time on earth (in this case a location in Australia).

    After this projection, the temperature of the projected map was summed at each frequency. Once this was coded, I add a series of “for” loops in my software to change the antenna’s latitude from -90˚ to 90˚, the time from hour 0 to 24, and the orientation azimuth from phi of 0˚ to 360˚. After plotting as a function of frequency, the curves were fitted with a second order power curve with the form: Ax^B+C. All of the curves and the corresponding residuals were plotted on the same figure for better comparison (Figure 5 and Figure 6 below). Once on the same plot, the curves that had an error larger than 0.05 K were eliminated. The last step was changing the time and the location simultaneously to determine the best combination of data collection of those two parameters – this can be seen in Figure 7. So far, our experiment site in Western Australia at -27 latitude is looking pretty good (at least for part each day)!

    Figure 5 - Temperature Sum For Different Latitudes

    Figure 5 – Temperature Sum For Different Latitudes


    Figure 6 - Residuals for Best Latitudes

    Figure 6 – Residuals for Best Latitudes


    Figure 7 - Best Latitude and Time to Collect Data

    Figure 7 – Best Latitude and Time to Collect Data

    This process, although easy to write out step by step, was quite particular. Taking hundreds upon hundreds of data points from an antenna and figuring out how to adapt the program that was written for the theoretical case was less than straight forward.

    So, is it abstract art or science??

    Plot of the Coordinates - This one is fun to look at!

    Plot of the Coordinates – This one is fun to look at!

    Another plot of the coordinate system that is just fun to look at!

    Another plot of the coordinate system that is just fun to look at!

     
  • raul_monsalve 2:38 pm on December 7, 2012 Permalink | Reply
    Tags: , chile, , , radio   

    Southern Hemisphere Again! 

    Hey gals and guys!! My name is Raul Monsalve, Chilean, and this is my first post on the ASU Explorers blog. Just like the other contributors, I will show you some of the exciting things we do at ASU as part of the cutting-edge research endeavors.

    I am currently a Postdoctoral Scholar; my undergrad degree is in electronics engineering and my PhD is in Physics, where I worked on a CMB polarization experiment called QUIET. With that background, it is obvious that I like instrumentation for radioastronomy and that is why I am enjoying a lot working at ASU in the exciting field of Low-Fewquency Cosmology.

    As you know by now (especially with all the experiences shared by José in previous posts), astronomy is a discipline conducted at an international level for several reasons, and therefore if you want to join this field you will become a world citizen sooner or later.

    As an example, last week I traveled to Chile to a conference on astronomical instrumentation organized and hosted by the Chilean Ministry of Foreign Affairs and several universities. Being one of the most developed countries in South America, Chile hosts an important amount of world-class telescopes because of its clear skies in several frequency ranges. Among others, telescopes such as ALMA, E-ELT, GMT, VLT, CTIO, CCAT, QUIET, CBI, APEX, ASTE, NANTEN, ACT, POLARBEAR, TAO, CLASS, have chosen Chile to observe from. Astronomy is indeed becoming the focus of Chilean support in the R&D department.

    Some of the ALMA antennas at an elevation of 16,500 feet in the Chilean Atacama desert.

    VLT optical and infrared telescope at an elevation of 8,645 feet in the Chilean Atacama desert.

    During this trip I did not visit any telescope because all my time was devoted to the conference. It was the first meeting of its kind in the country, and had the purpose of introducing the efforts of teams from several universities working on instrumentation. Government representatives also attended in order to present the different financial instruments available for astronomy research. They stressed the fact that support has been increasing year by year, and encouraged (young) people to make use of it. Many Chilean astronomers, engineers and students attended, as well as internationally renowned scientists. This gave everybody the opportunity to network and broaden their perspective.

    I gave a talk the third day of the conference about what we do best: Low-Frequency Cosmology. It served as an introduction to the topic to Chilean scientists, and also proposed the idea of the participation of Chilean institutions in this kind of studies, possibly in collaboration with ASU. From people’s reaction, I can say that the talk and the idea were very well received, and that people from important institutions are very interested in participating. In that sense, the trip was a total success!!.

    My talk on low-frequency cosmology at the Chilean Ministry of Foreign Affairs, with part of the audience.

    Round of questions after the talk.

    Chilean government palace, “La Moneda”, in Santiago. The view is from the top of the Ministry of Foreign Affairs building, where the conference was held.

     
  • josemanuelchavez 4:32 pm on December 5, 2012 Permalink | Reply
    Tags: , , , , , radio   

    Australia Recap + Deleted Scenes 

    These past two weeks have been the first of many things: first flight on American & Australian airlines (previously, I had only traveled on a Mexican airline) and the first time on a different continent.  We took one of the longest flights available and traveled to one of the most remote areas on Earth – which was precisely the point of this trip!

    One would think that this trip would show the vast differences between the U.S. and the ‘Land Down Under’.  Yet, I only noticed strong similarities throughout my stay.  Our flight over to Perth was akin to traversing the southern California countryside – plenty of discernible ranches with rambling roads along the way.  Other than the ‘Australian’ accent, which is not the same in all parts of the country, there aren’t too many disparities in the language.  I found the enunciation – with all its diversity – to be pretty awesome.  In contrast, it took me quite a while to get used to riding in the left lane – it’s like driving in a mirror image of the road!  Throughout the trip, I felt thoroughly welcomed and thrilled to be in a new land – scarcely feeling like a foreigner.  America and Australia are indeed siblings in the international spectrum.

    Another aspect of this trip that I enjoyed quite a lot was the fieldwork.  I have found going about the Australian outback, inspecting and mending instrumentation, to be incredibly fun.  It’s like playing in a giant sandbox that’s hundreds of square kilometers in size!  Yet, whether in the lab or a remote radio quiet zone, once you’re focused on what you’re doing, you quickly lose track of the setting.  In the field of astronomy, the entire world – nay, the entire universe – is our lab.

    Throughout the trip, I have observed the problem solving tactics of the other team members. With three PhD’s and a highly experienced technician constantly nearby, there’s always something to be learned.  I have noted their pedagogical tips and hope to apply what I’ve learned to tackle new problems.

    (One of my favorite quotes: “Don’t be a ‘guess-and-check’ engineer.  Be a scientist and solve this problem.”)

    From one west coast to another; a symphony of domestic and international flights, it has been a privilege and a pleasure to be your liaison throughout this trip.  Until next time, I hope you may again choose LoCo Airlines to reach your destination.

    Cheers!

    -Jose

    ________________________________________________________________________________________________________

    Deleted scenes:

    Foggy LAX

    Foggy LAX

    The behemoth that got us to Sydney - Boeing 747.

    The behemoth that got us to Sydney – Boeing 747.

    Our onsite LoCo engineer, Mr. Lizard.

    Our onsite LoCo engineer, Mr. Lizard.

    ASKAP radio telescopes aka giant mushrooms

    ASKAP radio telescopes aka giant mushrooms

    Always have a notebook handy - whether at the MRO or Mars.

    Always have a notebook handy – whether at the MRO or Mars.

    The team's glamour shot.  We come in peace.

    The team’s glamour shot. We come in peace!

    Giant sandbox

    Giant sandbox

    Caught me off guard

    Caught me off guard

    Like a kid in a candy store.

    Like a kid in a candy store.

    Representing the Sun Devils

    Representing the Sun Devils

    No gang signs please.

    No gang signs please.

    MWA core

    MWA core

    'roos on the run

    ‘roos on the run

    Go Devils! (I'm starting to sound like cheerleader aren't I?)

    Go Devils! (I’m starting to sound like cheerleader aren’t I?)

    On top of things.

    On top of things.

    This guy is a 24/7 explorer!  He creatively tied his camera to the end of a shoelace and fished a few shots inside a small cave.

    Hamdi is a 24/7 explorer! He creatively MacGyvered his camera to the end of a shoelace and fished a few shots inside a small cave.

    Don't get alarmed, it's just a flying camera riding on a kite.  No big deal.

    Don’t get alarmed, it’s just a flying camera riding on a kite. No big deal.

    Shh...

    Shh…

    Can you spot the emu/s?

    Can you spot the emu/s?

    Windy coast at Geraldton.

    Windy coast at Geraldton.

    Oh hey, there's the Opera House!

    Oh hey, there’s the Opera House!

    Until next time, Sydney!

    Until next time, Sydney!

     
  • josemanuelchavez 2:44 am on November 28, 2012 Permalink | Reply
    Tags: , , , , , radio   

    Day 5.2: Ariztralia 

    As we finish our fifth day in Australia, I am set with mixed feelings.  On one side, we are essentially done with most of the work that our trip was designated for.  On the other, we are a day closer to leaving this amazing country – which feels just like home, sometimes even better.

    View from the breakaway

    View from the breakaway

    We’ve stopped by the control building and Boolardy Station for the last time.  We are extremely thankful for their hospitality and assistance.  The food was simply second to none; the staff was extremely supportive and constantly let us borrow equipment (we made sure to hand everything back) while teaching us more about the Australian culture.  Lou and I practiced speaking bit of Mandarin on site, I’m sure it had been months since either of us had done so with another speaker.  It’s important to note how useful the control building was.  It has been, in many ways, our home base.  Let’s put it this way, if we were astronauts in near-Earth orbit, it would have been our ISS (International Space Station).

    Arriving at Geraldton

    Arriving at Geraldton

    After a four hour drive, we arrived at Geraldton.  A small resort town, it is right on the coast facing the Indian Ocean.  It’s been years since I’ve smelled the salty air; pleasant gusts of wind are constant reminders.  I’ve never been in this part of the world, yet it feels awfully familiar.  Tomorrow we will depart to Perth and then onto Sydney.  Cheers mate!

     
  • josemanuelchavez 9:51 pm on November 26, 2012 Permalink | Reply
    Tags: , , , , , radio   

    Day 5.1: Flying Cameras 

    Hello all!  Today we woke to another amazing breakfast and headed off to the MWA site.  We toured through all the tiles and climbed the nearby breakaway.  For the first time in the trip, we finally got some pictures of some kangaroos (or rather, “roos”).

    'roo radio explorers

    ‘roo radio explorers

    We then returned to the DARE/EDGES to take a final view of the set up. Lou, one of the MRO staff, let us borrow a compass which we used to measure the angle of the DARE antenna from North.  As he told us, this area has very little magnetic interference which helps us get very accurate measurements.   The angle was found to be about 19 degrees off.

    While part of the time was wrapping things up, Danny and I attached a camera to his kite and took aerial footage of the site.  After a couple of failed attempts, we finally got the kite to fly consistently and saved the video.

    Test run of the LoCo KiteCam

    Test run of the LoCo KiteCam

    Aerial view of EDGES

    Aerial view of EDGES

     

     
  • josemanuelchavez 9:30 pm on November 26, 2012 Permalink | Reply
    Tags: , , , , , radio   

    Day 4: It's LoCo Time! 

    G’day mates!  It seems like the Australian dialect has finally caught up to me.  With most of the fieldwork complete, we reviewed the glorious amounts of data that DARE/EDGES had produced.  Nothing alarming came up during the day, so we decided to stay in the homestead and organize our gear for our transit back home.  Truth be told, it was quite a good thing to stay in today, given that it was considerably warmer than the previous days.

    Representing ASU

    Part of the team went to Mullewa to pick up the new addition, Dr. Danny Jacobs.  Bringing new energy and supplies (a filter), Dr. Jacobs was promptly updated about the team’s work.

    Hard at work

    We are planning to go out (briefly) to the field again tomorrow.  The agenda is to measure the orientation of the DARE and EDGES systems  and to run a few more tests on the DARE receiver.

    Site satellite view

    It’s important to note about the warning that everyone who visits the MRO will gain weight.  Skeptical at first, I would like to conclude that this is in fact, true.  Imagine being offered multiple, delicious meals throughout day – there is simply no way to say no.  The perfect example is the local yellow lab who has been at Boolardy Station for a few years.  He happily trots around the encampment, taking breaks along the way, and nibbling on unidentifiable crumbs.

    Monty

    Today will be our last day here, we will depart tomorrow afternoon to Geraldton and onto the MWA meeting.

    With busy schedules, almost always something on the agenda, and families in different time zones – one often looses track of time.  But when asked what time it is, we respond: “It’s LoCo time here!”.

     
  • josemanuelchavez 5:59 pm on November 25, 2012 Permalink | Reply
    Tags: , , , , , radio   

    Day 3.2: Divide and Conquer 

    Mid-morning we had “smoko” (coffee break) – a delicious coconut cake with a sweet lemon frosting. Hamdi has become a huge fan of the butter out here (as he says, “MRO has the best butter in the world!  I am an MRO guy!”), so one of the MRO staff, Mike, brought Hamdi two bricks of butter for his smoko. However, we couldn’t convince Hamdi to eat that instead of the cake…

    Hamdi with his butter

    Possibly enthused by all the sugar, the team embarked to the field, ready to engage DARE/EDGES yet again.  Once at the site, Judd split us into teams: the A Team would deploy the EDGES receiver to a run a few tests while B Team would glue the DARE’s foam housing back together.  Not unlike a couple of special operations units, we performed our duties.  (Maybe next time we could do a parachute jump and land directly on site.)

    Inspecting the EDGES system in the control building

    Hamdi and I focused on running a few tests on EDGES, starting off by measuring the impedance.  We had to layout what seemed like elvish rope’s (Lord of Rings reference anyone?) worth of Australian extensions cables between the hut and the antenna.  In order to weatherproof the antenna, the team thriftily covered the receiver with a plastic bag and laid down an adhesive cover across the upper slits of the antenna.  With this complete, we took a sample of the spectrum and verified it looked comparable to a previous measurement.   Oddly enough, being able to see just a little RFI helped us validate the spectrum measurement again.  Spotting one of these man-made signals is a reassuring token that the antenna is functioning properly.  For example, occasionally detecting a spike around 120 MHz means that an airplane might be flying overhead.  With this healthy indication, the team left EDGES recording overnight.

    Running tests on EDGES

    The B squad directed their efforts to fortify DARE.  They had to make efficient use of the glue on hand, carefully positioning glue pellets along the along the walls.  Even the distinctive “scarred” side of the enclosure seemed to have healed well.  Not a field for the faint of heart, radio instrumentation sometimes proves injurious for interloping spiders and foam boxes.

    Tying down DARE

    Having received positive results and stabilized the devices, the team drove back to the homestead with a considerable weight off its shoulders and off the truck bed, literally.  We had less stuff to take with us – not as much to worry about.  Depending on the quality of data, we might not return to the site tomorrow and instead spend time analyzing the data.  All indications suggests that both experiments are being team players and producing splendid results.

    Discussing the preliminary data

    Rested and washed up, we had an amazing roast beef for dinner.  Complete with a side of bread, non-skinned potatoes, peas, and squash – a feast for champions.  Moreover, Hamdi finally caught up with his daily consumption of butter.  Slowly but surely, he conquered the golden cube – the reward of a day’s hard work.

     
  • josemanuelchavez 12:00 am on November 25, 2012 Permalink | Reply
    Tags: , , , , , radio   

    Day 3.1: Up and rrrrruning 

    On day three of this journey, the strategy was to place the DARE antenna back inside the foam box.  Sure enough, as soon as we had placed the antenna back on the foam supports, Hamdi noticed that one of the antenna terminals was broken.  This meant that we needed to re-solder the joint together.

    Inspecting the DARE system

    Rather than risk moving the antenna again, we constructed a makeshift lab in the outdoor desert so we could solder the joint in place.  Hamdi promptly began soldering in a meditative style that would have made his yoga instructor proud.

    Balancing stick position

    Once the terminal issue was fixed, the team did a quick spectrum measurement from 1-300 MHz in the hut.  We noticed that it looked considerably different.  There was plenty of power from the sky!  At first we thought the RFI look suspiciously low.  Although we are in a RFI-low area, there is still a small trace of things that we should see in the spectrum – such as occasional Orbcomm transmissions at 137 MHz.  After waiting a few minutes, we did indeed see these signals.

    Field lab

    It’s also nice to note that today has been considerably cooler than the previous days.  The wind helped keep the flies away and the pristine clouds were very welcomed.

    Hamdi proceeded on to taking a total power measurement.  First with the antenna connected and then with the load.  The input connection was connected to a splitter, which splits the signal in half.  We then have to compensate for this by adding 3 dB to both signals.  We recorded the total power produced by DARE when using the antenna to be -24.64 dBm and the load to be -28.46 dBm.

    DARE with our hut in the background

    With roughly half a day’s work already completed, we’ve analyzed some of data back in the control building. After a refueling lunch, we’ll go out again and wrap things up.

     
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