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: http://www.naic.edu/~astro/sdss7/handson_projects.shtml
Дата изменения: Unknown Дата индексирования: Fri Feb 28 04:46:18 2014 Кодировка: IBM-866 Поисковые слова: arp 220 |
All participants will take part in a “Hands-on Project” at the single-dish school. Mentored by a member of the NAIC or NRAO staff, each of you will join a team of 3 or 4 participants to perform a short pre-planned research-style observation. The participants will set up the observation, take the data, perform data reduction, interpret the results, and give a short presentation on the project on the last day of the School.
We ask that you review the 15 projects described below. At the bottom of this page you should then record your four preferred selections in the order of your preference. We apologize in advance if you do not get your first choice, as the number of participants per project is limited to 3 or 4.
Friday 1700 тАУ 2100 and Saturday 1700 - 2030
We will carry out measurements of CO at high-redshift from the infrared-bright H-ATLAS galaxies which are in their formative phases. Using the GBT and Zpectrometer backend, we will derive the redshift (i.e., the distance, and hence the luminosity) and measure the mass of molecular gas fueling the star-formation in these nascent galaxies. This project requires the Ka-band receiver and reasonable weather. If the weather is not appropriate, we would carry out HI observations of the GOALS LIRGs/ULIRGs which represent local analogs of the high-redshift infrared sources.
Friday 0130 - 0600
You will use the GBT to map the continuum emission from the Cygnus Loop, and in comparison with maps at a different frequencies, determine the nature of the observed radio emission.
Sunday 0230 тАУ 0700 and 0745 - 0930
UGCA 86 is a gas rich dwarf irregular galaxy that resides a mere 71 kpc, projected on the sky, from its nearest neighbor, face-on spiral galaxy IC 342. It has been speculated that UGCA 86 is interacting with IC 342, however, until recently, there was no definitive evidence for an interaction. Two HI tails extending out from IC 342 and UGCA 86, respectively, reaching in the direction of the other, were discovered with the GBT, thus proving that the two galaxies are interacting. The GBT map shows that the HI emission from the tails extends off the edge of the mapped area and it is not clear whether these structures join together to form a continuous HI bridge. This summer school project will map a 2 degree x 1 degree region south of the previous GBT map to follow the HI emission of the tails and assess whether they form a connected HI bridge.
Thursday 2130 тАУ Friday 0130
The Milky Way provides the closest vantage point to study how stars form. Because we reside within the Milky Way, the interpretation of these observations is complicated by the difficulty of determining distances to star-forming regions and thus being able to derive fundamental physical properties like luminosity and size. In this project, you will use the GBT to observe radio recombination line emission from the ionized gas surrounding young massive stars to determine the distance to the star-forming regionsin the Milky Way. You will also compare properties of the dust and gas out of which the young massive clusters formed using radio and infrared data.
Saturday 0000 - 0430
G28.17+0.05 is a giant atomic cloud containing 100,000 solar masses of atomic gas. At the core of this cloud is one of the densest Infrared Dark Clouds, IRDC G28.35+0.05. IRDC G28.35+0.05 is a starless core that is in the earliest stages of forming a massive stellar cluster. This cloud is the perfect place to study the transition from atomic to molecular gas. This project will map the cloud in HI and OH with the GBT to highlight differences in where the atomic and molecular gas appear in the outer parts of the cloud. A map of other molecules (HC7N, HC9N, HCCCN) using the GBT X-band receiver will also be made to highlight the more advance chemistry that occurs in the cores of molecular clouds.
Friday 2100 - 2400
Recently McClure-Griffiths et al published an ApJ Letter describing the discovery of a population of HI clouds in the Galactic Center with properties suggesting that they are entrained in a ~2000 km/s wind from the Galactic nucleus. These clouds were detected with the ATCA at an angular resolution of 2.4 arcmin and an rms noise of 0.7 K. Typical peak line temperatures in the 21cm line are not much more than 3-sigma, or 2 K. It is not clear what these clouds are, nor if the ATCA observations have detected the entire cloud or only the cold cores. The objects might be surrounded by more extensive, lower brightness HI regions, perhaps with a larger linewidth as expected from a two-component ISM cloud.
For this project we will be making a brief census of these clouds with the GBT simply to compare the mass and line shape with that detected by the ATCA.
Thursday 1900 - 2130
Note тАУ This project will be run alongside project AO-3
This project is designed to demonstrate the fundamentals of spectral line observing. Two separate “hands-on” groups will observe the 21-cm HI emission of the same galaxies with either the GBT or Arecibo radio telescopes. At Arecibo, we will simultaneously search for the 18-cm mainlines of the OH molecule in these galaxies. This projectis to carry out the GBT observing. All chosen targets are known to have HI distributions that extend to distances comparable to, or beyond, the angular size of the Arecibo beam. After data reduction, the Arecibo and GBT spectra, and parameters derived from these, will be compared for agreement/disagreement. Beam maps will also be made with the Arecibo telescope (and hopefully the GBT telescope) in order to provide both beam patterns and sizes.This exercise will illustrate the fundamentals of spectral line observing, including restrictions due to beam sizes, side lobes, etc.
All the spectral-line observations will be made with the position-switching technique. In this, the target position is observed first, followed by a blank-sky (off-source) position. The blank-sky observation is used to remove atmospheric and system noise, and to bandpass calibrate the on-source spectrum. With single dish telescopes, position switching provides the simplest means to eliminate standing waves and other instrumental effects from spectra.
Friday 1830 - 2245
An Ultra Luminous Infrared Galaxy (ULIRG) is a galaxy in which gas is turning into stars extremely rapidly within its circum-nuclear volume. Such starbursts are often triggered by external dynamical disturbances such as galaxy mergers. The dust heating associated with these intense bursts of star formation within giant molecular clouds can produce hugely increased IR luminosity and conditions favorable for radio maser emission. The strong 18-cm OH megamaser emission in some of these galaxies is many orders of magnitude more luminous than its counterpart in our Galaxy (Darling & Giovanelli, 2002, AJ, 124, 100.)
The prototype ULIRG, Arp 220, has recently been found to possess a rich molecular-line spectrum between 1.1 and 10 GHz (Salter et al., 2008, AJ, 136, 389). Some of the molecular species detected are considered to be pre-biotic. To see how unusual Arp 220's spectrum is for this class of galaxy in general, a sample of 20 other ULIRGs have now been observed between 4.3 and 5.3 GHz. Preliminary analysis has shown two of the twenty, IC 860 and Zw 049.057, to have remarkably similar line spectra to Arp 220.
In this Hands-on-Project, the observing team will take spectra between 1.1 and 1.75 GHz for IC 860, Zw 049.057 and another peculiar galaxy, Arp209, to see to what extent their spectra over this lower frequency range, (usually referred to as the “L-Band”) resemble that of Arp 220. L-Band contains potential detections for neutral atomic hydrogen, HI (1420 MHz rest frequency), main-line OH molecules (1665 & 1667 MHz), satellite-line OH (1612 & 1720 MHz) isotopic 18OH (1637 & 1639 MHz), Formic Acid (HCOOH; 1638 MHz), HCN (1346 MHz) and HCO+ (1270 MHz). Detectability of some of these transitions is likely to be affected by the presence of radio frequency interference (RFI) which the team needs to distinguish from celestial emissions. Despite RFI, a number of line detections are anticipated.
A C-band spectrum (4 - 5 GHz) of Arp 209 will also be recorded as a detection experiment for new Cm-wavelength transition in this galaxy.
Friday 2245 тАУ Saturday 0245
Measuring magnetic fields in astronomy requires measuring polarization. Spectral lines exhibit Zeeman splitting, the degree of which tells the in-situ field strength of the emitting gas. Continuum sources exhibit Faraday Rotation, which tells the total line-of-sight product of the magnetic field strength times the electron volume density.
Polarization measurements are more involved than ordinary total-intensity measurements, requiring specific observing and calibration techniques. Most astronomers regard them as too hard and would rather acccumulate easy results so that they can write lots of meaningless papers. Real astronomers do the difficult stuff (which includes not just polarization but, also, other not-so-easy types of measurement) and write fewer papers, but ones that are meaningful. In the case of magnetism, it is one of the three major forces on intersttelar gas, but is usually ignored because its pressure forces are anisotropic and somewhat complicated.
We will observe some spectral lines for Zeeman splitting. These lines originate in OH masers associated with cool stars, and near the stellar surface the field strengths can be quite intense so that Zeeman splitting can be quite prominent. We will also observe some continuum sources for Faraday rotation. We will choose sources from a large survey of Faraday rotations, a particular set of sources whose survey results are probably incorrect because their Faraday rotations are so large; our purpose is to get a feel for what kind of errors might occur in this survey.
Saturday 1900 - 2245
Note тАУ This project will be run alongside project GBT-7
This project is designed to demonstrate the fundamentals of spectral line observing. Two separate “hands-on” groups will observe the 21-cm HI emission of the same galaxies with either the GBT or Arecibo radio telescopes. At Arecibo, we will simultaneously search for the 18-cm mainlines of the OH molecule in these galaxies. This project (AO-5) is to carry out the Arecibo observing. All chosen targets are known to have HI distributions that extend to distances comparable to, or beyond, the angular size of the Arecibo beam. After data reduction, the Arecibo and GBT spectra, and parameters derived from these, will be compared for agreement/disagreement. Beam maps will also be made with the Arecibo telescope (and hopefully the GBT telescope) in order to provide both beam patterns and sizes.
This exercise will illustrate the fundamentals of spectral line observing, including restrictions due to beam sizes, side lobes, etc. All the spectral-line observations will be made with the position-switching technique. In this, the target position is observed first, followed by a blank-sky (off-source) position. The blank-sky observation is used to remove atmospheric and system noise, and to bandpass calibrate the on-source spectrum. With single dish telescopes, position switching provides the simplest means to eliminate standing waves and other instrumental effects from spectra. The Arecibo beam maps will be produced via continuum “spider scans”.
Saturday 2245 тАУ Sunday 0245
OH maser emission is frequently observed from high-mass star formation regions. The best studied maser transitions are those of the 2Π3/2 (J=3/2) ground state at about 1.65 GHz. However, maser emission in the 2Π3/2 (J=5/2) and 2Π1/2 (J=1/2) transitions, (at frequencies of about 4.7 and 6.0 GHz respectively), have sometimes been detected, though little studied. Recently, maser emission in the 2Π1/2 (J=1/2) transitions has been detected in the luminous-IR galaxy, NGC 660.
The 2Π1/2 (J=1/2) triplet of lines fall at 4660, 4750 and 4765 MHz. The 4750 MHz feature is the main-line (F=0–C0 and 1–C1), with the 4660 MHz (F=0–C1) and 4765 MHz (F=1–C0) transitions being the satellite-lines. In conditions of Local Thermal Equilibrium (LTE) the intensities of the three lines, (in order of increasing frequency), are in the ratio 1:2:1. For maser emission, the intensity ratios can differ wildly from the LTE values.
The present “Hands-on-Project” will make a small survey of the three 2Π1/2 (J=1/2) OH lines in a number of Galactic environments. The targets are planned to be sources associated with:
As well as the three excited lines of OH, we will simultaneously observe transitions of HCN(v2=1), H2CO, H213CO, and two Hnα (hydrogen recombination) lines.
Sunday 0945 тАУ 1315
The planetary radar system will send short pulses at S-band of one megawatt to Mercury to obtain echoes from the planet's surface. The sensitivity of the radar system and the telescope is sufficient to obtain significant echoes not only from the nearest part of the planetary disk but also from more distant regions. We will carry out a Fourier analysis of the echoes' spectral compositions to determine the rotation rate of Mercury.
During hands-on data-reduction times
Introduction to CASPER* hardware a software tools, particular focus in ROACH 1, iADC and katADC. We are going to be using the MSSGE** toolflow to generate configuration files for the FPGA (Field Programmable Gate Array), and Python scripts for configuration and data capture. The intention is to digitize a simulated bandpass (filtered noise source), do some digital signal processing (algorithms are going to be decided on Wed, 10 Jul) and send and capture the data in a computer.
* CASPER: Collaboration for Astronomy Signal Processing and Electronics Research
** MSSGE: Matlab/Simulink/System Generator/EDK
Sunday 1900 - 2245
Students will formulate a question or hypothesis regarding the neutral hydrogen (HI) properties of galaxies as they relate to other characteristics. They will select a sample of galaxies to observe for testing the hypothesis. Possible hypotheses are listed below.
Note that there will be time to observe perhaps at most 10-12 galaxies. You will need to select galaxies that are observable within the allotted observing time (an LST range of 1400 тАУ 1745). You will draw up a list of galaxies to be observed, devise an observing strategy, and prepare the observing setup.
HI properties that can be derived from the observations include hydrogen content, total hydrogen mass, redshift, line width, rotational velocity, and line profile morphology.
Possible questions that might be considered are:
Students are not constrained to these questions only; they are encouraged to formulate their own ideas. But note that there is limited time for the project, so best to keep it simple!
A good resource to consult is NED (the NASA Extragalactic Database), for searching for galaxies that have certain selected properties.
Students will learn how to configure the Arecibo system for observing HI. They will need to prepare a list of galaxies to be observed, giving:
They will also need to decide:
Resources for using Arecibo include the Astronomer's Guide, which gives the capabilities of the receivers and back ends, and the available observing modes. The guide also details how to calculate the necessary integration times. Further instruction on how to set up and carry out the observing will be given by local staff.
Sunday 2245 - 0200
Pulsars, neutron stars with rotation periods ranging from a few seconds down to little more than a millisecond, are known for behaving like accurate natural clocks. They emit a radio pulse on each rotation, with the intervals between successive pulses being very precise. This property can be exploited to study the exotic state of matter in the interiors of neutron stars, to detect gravitational waves, and to test General Relativity and alternative theories of gravity.
The PALFA survey at Arecibo has been searching for pulsars in the Galactic plane since 2004 and has so far discovered 116 new pulsars. There are typically many signals in PALFA survey data that look like potential pulsars, though some or even most of these signals may be caused by instrumental noise or pulsed terrestrial radio frequency interference. Before we can be sure a candidate pulsar is real, it has to be detected at least once after the initial survey pointing that recorded the signal. We will observe pulsar candidates from the PALFA survey and try to detect their periodic emission. This project is science in action and our findings may be included in a future publication: there have been no attempted confirmation observations on these candidates so far and we do not know whether they are real pulsars.
Please indicate your four preferred hands-on projects in the order of your preference: