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. (B)</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. (D)</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 (D)</p> Signup and view all the answers

How is the luminosity of a star defined?

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

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

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

What measures the reflectance of the dust grain?

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

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

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

What bands are conventionally used for estimating extinction?

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

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

<p>0.60 (A)</p> Signup and view all the answers

What characterizes the interstellar extinction curves mentioned?

<p>They exhibit a 'bump' around 2175 Å. (A)</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 (B)</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. (D)</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 (A)</p> Signup and view all the answers

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

<p>F0V (D)</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 (C)</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 (C)</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 (B)</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 (B)</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 (C)</p> Signup and view all the answers

Flashcards

Interstellar Extinction

A measure of how much light from a star is absorbed by interstellar dust and gas.

Color Index

A measure of how much brighter a star appears in one color band compared to another.

Spectroscopic Parallax

A method to determine the distance to a star by comparing its apparent magnitude with its absolute magnitude, corrected for interstellar extinction.

Extinction Curve

The relationship between extinction and color index.

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2175 Å Bump

The wavelength at which the extinction curve shows a peak, usually around 2175 Å.

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B-V Color Index

A standard color index used for interstellar extinction calculations.

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k(B-V)

The relationship between the extinction coefficient (k) and the color index (B-V).

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Standard Candle Method

A method that uses a star's color index and absolute magnitude to estimate the distance, taking into account extinction.

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Dust grain thermal equilibrium

The process where a star's radiation heats a dust grain, causing it to reach a balance between the energy it absorbs and emits.

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Dust polarimetry

The study of the characteristics and properties of cosmic dust using polarized light. This technique allows for the detection of dust presence, its alignment, and even its composition.

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Mapping Galactic magnetic fields

The use of dust polarimetry to study the large-scale magnetic fields within galaxies. Dust grains align with magnetic fields, creating detectable polarization patterns.

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Radio emission from supernova dust

The process where dust particles in a supernova remnant, like Cas A, radiate strongly at radio wavelengths due to their interaction with electrons.

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Brown dwarf meteorology

The process of studying the atmospheres of brown dwarfs using polarimetry. Dust grains in these atmospheres are detectable due to their polarization signature.

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Blackbody Distribution Function

The energy emitted by a blackbody follows a specific distribution function based on its temperature. This means that the amount of energy emitted at different wavelengths depends on the object's temperature.

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Dust Grain Energy Absorption

The process of a dust grain absorbing energy from a star's radiation, with the amount of energy absorbed determined by the grain's size, albedo, and distance from the star.

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Fraction of Energy Reaching Dust Grain

The fraction of the star's total emitted energy that reaches the dust grain at a specific distance. This is calculated by considering the star's luminosity and the surface area of the grain compared to the sphere of radiation.

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Fraction of Energy Absorbed

The fraction of the incident radiation that is absorbed by the dust grain, dependent on the grain's albedo (reflectivity).

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Power Absorbed by Dust Grain

The power absorbed by the dust grain is determined by the fraction of energy absorbed (albedo), the fraction of energy reaching the grain, and the star's initial power.

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Dust Grain Heating

The process where a dust grain absorbs energy from a star and re-emits it as infrared radiation.

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Dust Grain Equilibrium Temperature

The temperature a dust grain reaches when it is in equilibrium with the energy it absorbs from a star, determined by the star's temperature, size, and the distance to the dust grain.

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Dust Grain Albedo

The ratio of the amount of light reflected by a dust grain to the amount of light absorbed by it.

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Dust Extinction

A method to estimate the distance to a star by considering the dimming of its light due to interstellar dust.

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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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