PH222 - Astrophysical Concepts Quiz
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Questions and Answers

What is significant about the atmosphere of L-dwarfs in the context of dust formation?

  • L-dwarfs do not contribute to understanding meteorological phenomena.
  • They are entirely devoid of dust grains.
  • Their atmospheres allow for detectable polarimetric signatures of dust grains. (correct)
  • They have the lowest temperatures among brown dwarfs.

    • Which event is associated with the bright radio source Cas A?

  • Its supernova remnant is located 3.4 kpc away. (correct)
  • It is primarily studied due to its excessive dust emissions.
  • Cas A is considered a recent astronomical phenomenon.
  • It was observed to explode in the 1800s.

    • What role does dust play in the study of large scale magnetic fields in the galaxy?

  • Dust does not affect the measurement of magnetic fields.
  • Only dust particles close to the star contribute to field mapping.
  • Dust can be used to influence the magnetic polarity.
  • Dust polarization measurements assist in mapping magnetic fields. (correct)

    • What does the DART mission specifically involve relating to dust?

    <p>It creates a dust plume through the impact on an asteroid moon.</p> Signup and view all the answers

    In thermal equilibrium, what relationship is expected between a dust grain's emitted energy and the energy it absorbs?

    <p>They are equal in value.</p> Signup and view all the answers

    What determines the blackbody distribution function of energy emitted and absorbed?

    <p>Temperature of the dust grain and star</p> Signup and view all the answers

    How is the luminosity of a star defined?

    <p>$L = 4 heta^2 T^4$</p> Signup and view all the answers

    What is the fraction of the surface area radiated to the dust grain defined as?

    <p>$F = \frac{4\pi d^2}{\pi r^2}$</p> Signup and view all the answers

    What measures the reflectance of the dust grain?

    <p>Albedo of the dust grain</p> Signup and view all the answers

    What is the power absorbed by the dust grain expressed as?

    <p>$P_{absorbed} = (fraction absorbed) \cdot (fraction at d) \cdot (initial power at the star)$</p> Signup and view all the answers

    What can be inferred if a means of quantifying the ISM's extinction effect is available?

    <p>The distance between us and the star can be inferred.</p> Signup and view all the answers

    What bands are conventionally used for estimating extinction?

    <p>B and V bands</p> Signup and view all the answers

    What is the value yielded from the equation = (11.0 - 10.1) - (0.30)?

    <p>0.60</p> Signup and view all the answers

    What characterizes the interstellar extinction curves mentioned?

    <p>They exhibit a 'bump' around 2175 Å.</p> Signup and view all the answers

    What is the final value of the distance in parsecs calculated from the expression 10.1 - 3.0 + 5 - 1.86?

    <p>112 pc</p> Signup and view all the answers

    How can the extinction effect of the ISM specifically vary?

    <p>It varies based on environmental conditions in galaxies.</p> Signup and view all the answers

    When calculating the extinction using the color index, which value is subtracted?

    <p>The intrinsic brightness of the star</p> Signup and view all the answers

    Which spectral class is exemplified by the F0V star in the calculations?

    <p>F0V</p> Signup and view all the answers

    What is the relationship between the distance of a dust grain from a star and its temperature?

    <p>Temperature decreases with the square of the distance</p> Signup and view all the answers

    What is the calculated temperature of a dust grain 0.01 pc away from the Sun with a solar temperature of 5772 K?

    <p>6.13 K</p> Signup and view all the answers

    Which law is used to determine the peak emission wavelength of a dust grain's temperature?

    <p>Wien's Law</p> Signup and view all the answers

    What role does dust play in the formation of solid objects in space?

    <p>Dust serves as a substrate for complex chemistry and solid object formation</p> Signup and view all the answers

    How does dust extinction affect distance estimation in astronomical observations?

    <p>It needs to be factored in to estimate distances more accurately</p> Signup and view all the answers

    Study Notes

    PH222 - Astrophysical Concepts

    • Course title: PH222 - Astrophysical Concepts
    • Instructor: Aaron Golden
    • Institution: Centre of Astronomy, School of Natural Sciences, University of Galway

    Last Time

    • Interstellar Medium (ISM) impact on light is wavelength dependent (∝λ)
    • Spectral class, expected spectral energy distribution, and observed distribution are used to estimate color indices.
    • Spectroscopic parallax can be used to determine stellar distances when accounting for wavelength-dependent extinction within the ISM

    Spectroscopic Parallax with Extinction I

    • If extinction is wavelength-dependent, observations in B and V bands can be used to calculate distances
    • Equations shown to derive and use these relationships
    • The difference in magnitudes (B - V) can be observed and used to calculate the difference in extinction (AB - Av)

    Spectroscopic Parallax with Extinction II

    • The total-to-selective extinction ratio (R) is used to calculate Av (visual extinction) and can take values from 3.1 to 6, depending on the galaxy environment.
    • Equation 2 can be used to calculate distance (d)

    Spectroscopic Parallax with Extinction III

    • Observations of a star identified as a F0V star (absolute magnitude My = +3.0 and colour index B-V = +0.30).
    • Apparent magnitudes m'B = +11.0 and m'V = +10.1 are observed
    • Calculate the visual extinction (Av) and distance (d).
    • The total-to-selective extinction ratio R is 3.1
    • Visual extinction (Av) is 1.86
    • Distance (d) is 112 parsecs (pc)

    Interstellar Extinction Curves

    • The actual value of R (total-to-selective extinction ratio) varies in different galaxy environments.
    • The 'bump' around 2175 Å in the curves suggests graphite or carbonaceous dust is a factor

    Dust Grains I

    • Dust grains compose approximately 1% of the interstellar medium (ISM) by mass
    • Size estimation by examining wavelength dependence of extinction.
    • Size >> wavelength: geometric optics apply.
    • Size ≈ wavelength: diffraction effects are significant.
    • Size variations from about 1 to 100 nm

    Dust Grains II

    • Dust grain shape can be determined by their ability to polarize reflected light.
    • Asymmetrical shapes (cigar or disk-like) are probable.
    • Interstellar magnetic fields likely align dust grains

    Dust Grains III

    • Composition of grains by examining absorption Spectra.
    • Silicates (SiO, SiO2) and water give broad IR absorption lines.
    • UV extinction likely from carbon.
    • Dust mix of large "dirty ice" grains (silicates and water) and smaller graphite grains (carbon).
    • Possible multi-layered structure.

    Dust Grains IV

    • Electric charge of dust grains depends on the dominant charging mechanism.
    • High extinction regions: charging via charged particles sticking to the surface.
    • Photoelectric effect: produces a positive charge.
    • Overall ISM expectation is to be neutral; gas charge balances grain charge.

    Dust Grains V

    • Dust grain temperature depends on distance from nearby stars.
    • Equating absorbed power and radiated power yields an equation for dust grain temperature in terms of star properties
    • The temperature of the dust grain is in the region of 6.13K when observing a dust grain 0.01pc away from the Sun.

    Additional Topics

    • Cas A Supernova Remnant: observations and data
    • OSIRIS-REx mission and asteroid Bennu sample collection.
    • DART mission and effects of dust plumes.
    • Different aspects of DIY dust formations discussed.
    • Detecting exoplanetary oceans.
    • Studying the weather on brown dwarfs by using polarimetry techniques
    • Mapping the large scale magnetic field of the galaxy menggunakan pengukuran polarisasi debu.

    Wrap-Up

    • Review of interstellar medium components between our solar system and α Centauri
    • Discussion of factors influencing dust distribution and composition in galaxies.
    • Importance of dust extinction in distance measurements
    • Role of dust as a substrate for complex chemistry.

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    PH222 - Astrophysical Concepts PDF

    Description

    Test your knowledge on the impact of the interstellar medium on light and the techniques used in spectroscopic parallax to determine stellar distances. This quiz will cover concepts like wavelength-dependent extinction and color indices. Prepare to dive into the intricacies of astrophysical observations and calculations.

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