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  • Phys 415 Assignments and Tutorials
    Regardless of your decision in b above let us now assume that all of the emission is synchrotron emission Use the minimum energy criterion to calculate the minimum energy U min the minimum magnetic field H min and the lifetime of the particles tau at the chosen position Assume that the ratio of heavy particles to electron energy k 50 and use lower and upper frequency cutoffs of 10 7 Hz and 10 11 Hz respectively The distance to the source is 24 6 Mpc d The standard equations assume spherical symmetry For the position you chose is spherical symmetry a good assumption or not Explain If not what different geometry would you choose e g slab cylinder other Would adopting this different geometry increase decrease or have no effect on the results for U min H min tau e A typical supernova remnant SNR radiates 10 49 ergs of energy in the radio continuum and we might expect several hundred SNRs to occur in any given open cluster or OB association over the lifetime of the cluster which is about 3x10 7 yr Supernovae of the type which produce SNRs are not known to occur outside of clusters Assuming

    Original URL path: http://www.astro.queensu.ca/~irwin/phy415/assn2.html (2016-02-13)
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  • Phys 415 Assignments
    source at a given velocity v in units of Jy dv is an elemental velocity increment in units of km s 1 and M HI is in units of M sun Int refers to integration of the flux density over velocity v b The accompanying figure shows the HI global profile of the edge on galaxy NGC 5775 solid curve and its nearby face on companion NGC 5774 dotted curve as determined from VLA observations in the 21 cm line of HI These are plots of the continuum subtracted HI flux density of each galaxy as a function of velocity The flux density in mJy is given for each velocity channel in a table at the right Assume that both galaxies are at the same distance of 24 6 Mpc and compute the HI mass of each galaxy c From the same curves can you compute or at least estimate the total dynamical mass of each galaxy Explain If so compute this mass d NGC 5774 is considerably smaller and fainter than NGC 5775 as indicated by its fainter apparent blue magnitude i e m B 11 25 for NGC 5775 and m B 12 47 for the fainter NGC

    Original URL path: http://www.astro.queensu.ca/~irwin/phy415/assn3.html (2016-02-13)
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  • Phys 415 Assignments
    its D Configuration in New Mexico for the continuum observation and the Nobeyama Radio Observatory NRO 45 m antenna in Japan for the line observation Your concern is that the proposed observations might require too much observing time to be considered seriously by the respective Time Allocation Committees at these telescopes From experience you know that you are unlikely to be granted more than 36 hours at either telescope simply because of competitive pressure from other proposals You also need to remember that once the observing time has been computed you must also allow for more time for overheads that is additional time for pointing calibrations etc Thus whatever time is calculated needs to be increased by about 25 for the VLA and about 30 for NRO a Observations of thermal Bremsstrahlung emission using the VLA An observing wavelength of 1 3 cm should be short enough to ensure that any foreground or background synchrotron flux is negligible As no previous radio continuum measurement has been made you do not know the flux density of the source and must estimate it based on some initial guess of the density HII region densities can span a wide range see class notes but to ensure that the source will be detected you need to do a calculation of the source s flux density using the lowest value for density The VLA will produce a map showing a variation in brightness across the circular source but to calculate the expected flux density in a beam simply take the total flux density of the source divided by the number of beams on the source to obtain an average flux density per beam You would like to detect this average value at a signal to noise S N of 100 1 Determine the amount of

    Original URL path: http://www.astro.queensu.ca/~irwin/phy415/assn4.html (2016-02-13)
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  • Phys 415 Assignments
    can t be done using ordinary techniques Who is doing this and what plans are in the works for future VLBI Some possible starting points for information are web sites http www nfra nl jive evn evn html http www haystack mit edu http ivscc gsfc nasa gov http www nrao edu vlba html CAPABIL aas vlbacap index htm http www jb man ac uk vlbi and or see the

    Original URL path: http://www.astro.queensu.ca/~irwin/phy415/assn5.html (2016-02-13)
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  • Phys 433/813 Assignment 1
    each star and impose a limit of m V 18 creating a magnitude limited sample Plot a graph of M V versus distance for the magnitude limited sample and comment on the resulting illustration of the Malmquist bias d Plot a graph of Φ M V versus M V for the magnitude limited sample on the same plot as a above e Fit a Gaussian to each of the two curves of part d and for each curve solve for the absolute magnitude of the peak and for σ How well does a Gaussian describe the data Should you restrict the magnitude range for a better fit f Compute the mean absolute magnitude of the magnitude limited sample M V m and compare it to the peak of the original sample M V 0 How does your value of σ V m compare with σ V What do you expect for a uniform density and Gaussian distribution and how do your results compare g Suppose we had restricted the data set to the luminosity function of the main sequence Comment as to what you might expect for such a case rather than the general luminosity function as was considered here 2 The Malmquist bias for a declining vertical distribution Do problem 3 6 in the text For this problem you need V N ν 0 where ν 0 is the local space density of stars V is the volume N dn is the total number of stars reached by the survey and the vertical density distribution ν ν 0 exp z h The radial part of your integration will be out to a limiting distance s lim Instead of reproducing Table 3 17 just calculate the effective volume for M 3 0 when m lim 2 5 and 6 0

    Original URL path: http://www.astro.queensu.ca/~irwin/phy813/assignments/assignment1.html (2016-02-13)
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  • Phys 433/813 Assignment 2
    for your limits With a 3 d plotting routine you should be able to explore parameter space and view the Milky Way from a variety of angles b Integrate your function and see if you can reproduce the total luminosity L sun for the disk and bar given in the same table c To convert from L band IR luminosity to total mass we need an estimate of the global

    Original URL path: http://www.astro.queensu.ca/~irwin/phy813/assignments/assignment2.html (2016-02-13)
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  • Phys 433/813 Assignment 3
    explain a flat rotation curve For this problem assume that the disk of the Milky Way has circular motions only a Suppose the Galaxy consisted of a disk only described by the Kent Dame Fazio 1991 model see previous hand out What functional form γ R would the mass to light ratio have to take in order for the rotation curve to be flat Comment on how realistic or unrealistic you expect this to be This table may be helpful b Suppose the law of gravity were modified see for example Bottema et al 2002 A A 393 453 such that g n g μ where g n GM R 2 refers to Newtonian acceleration g is the modified acceleration and the factor μ is given by μ g a 0 1 g a 0 2 1 2 where a 0 9E 9 cm s 2 Thus if g 0 then μ g a 0 and if g a 0 μ 1 For the same disk distribution as in a and assuming a constant global value in the disk for γ find V R out to 25kpc for such a case and comment on the results c Suppose in addition

    Original URL path: http://www.astro.queensu.ca/~irwin/phy813/assignments/assignment3.html (2016-02-13)
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  • Cooling Flows
    are not transient features and must exist for lifetimes of greater than a billion years The radiation from the cooling flow clusters at lower energy wavebands does not give any strong indication of the cooling flow There is a slight amount of extra blue light from the central region of the flow which peaks along any radio lobes generated by a central AGN It is worth noting that 71 of cD galaxies located in cooling flows are radio loud compared with only 23 of those not associated with cooling flows The conclusions to be drawn from this fact is that the mass accretion from the flow is associated with the radio emission In addition the Faraday rotation and depolarization of the emission allows us to map the magnetic field and the pressure within the ICM Both are seen to increase toward the center of the flow This is consistent with the collapse of a hot ionized gas that is collapsing to a form a higer density region Ideal magnetohydrodynamic theory requires magnetic fields to be frozen in or move with the fluid As the gas collapses and concentrates near the central galaxy the field is similarly concentrated This has also been used to explain a diffuse radio signal present around some cooling flow clouds In summary The x ray waveband shows a diffuse cloud of gas with a central peak of radiation Optical wavebands show an excess of blue light toward the center of the flow This light usually peaks along any radio lobes present in the galaxy and can be well modelled by B5 stars or a quasar like spectrum Additionally there are a number of prominent emission lines from metals Cooling flow galaxies frequently host strong central radio sources Some also show a weaker radio halo which may be caused by relativistic particles accelerated by the compression of magnetic field lines trapped in the collapsing gas All these observations support the idea of a diffuse cloud of gas collapsing as thermal pressure is removed III Theoretical model As clouds of intergalactic gas collapse under the influence of gravity they convert their gravitational potential energy to internal energy and heat up The gas then proceeds to cool by radiating away its stored internal energy If this gas cools quickly then it is no longer visible at present However in some clusters and large galaxies the cooling is slow enough to persist until now The slow cooling allows the gas to enter a quasi hydrostatic equilibrium The hot gas exists at close to the virial temperature of 10 7 K As the gas cools it is no longer be supported by pressure This causes a slow inflow It is this inflow of gas that is called the cooling flow How long does the cooling take What cooling timescales are required for us to observe the hot gas The time for cooling by thermal bremsstrahlung radiation is related to both the temperature and the density of the gas with t cool

    Original URL path: http://www.astro.queensu.ca/~irwin/phy814/cooling1.html (2016-02-13)
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