This article is about astronomical graphs of brightness variations. For photosynthetic response graphs, see Light curve (botany).
In astronomy, a light curve is a graph of light intensity of a celestial object or region as a function of time, typically with the magnitude of light received on the y axis and with time on the x axis. The light is usually in a particular frequency interval or band. Light curves can be periodic, as in the case of eclipsing binaries, Cepheid variables, other periodic variables, and transitingextrasolar planets, or aperiodic, like the light curve of a nova, a cataclysmic variable star, a supernova or a microlensing event or binary as observed during occultation events. The study of the light curve, together with other observations, can yield considerable information about the physical process that produces it or constrain the physical theories about it.
Graphs of the apparent magnitude of a variable star over time are commonly used to visualise and analyse their behaviour. Although the categorisation of variable star types is increasingly done from their spectral properties, the amplitudes, periods, and regularity of their brightness changes are still important factors. Some types such as Cepheids have extremely regular light curves with exactly the same period, amplitude, and shape in each cycle. Others such as Mira variables have somewhat less regular light curves with large amplitudes of several magnitudes, while the semiregular variables are less regular still and have smaller amplitudes.[1]
The shapes of variable star light curves give valuable information about the underlying physical processes producing the brightness changes. For eclipsing variables, the shape of the light curve indicates the degree of totality, the relative sizes of the stars, and their relative surface brightnesses.[2] It may also show the eccentricity of the orbit and distortions in the shape of the two stars.[3] For pulsating stars, the amplitude or period of the pulsations can be related to the luminosity of the star, and the light curve shape can be an indicator of the pulsation mode.[4]
Light curves from supernovae can be indicative of the type of supernova. Although supernova types are defined on the basis of their spectra, each has typical light curve shapes. Type I supernovae have light curves with a sharp maximum and gradually decline, while Type II supernovae have less sharp maxima. Light curves are helpful for classification of faint supernovae and for the determination of sub-types. For example, the type II-P (for plateau) have similar spectra to the type II-L (linear) but are distinguished by a light curve where the decline flattens out for several weeks or months before resuming its fade.[5]
In planetary science, a light curve can be used to derive the rotation period of a minor planet, moon, or comet nucleus. From the Earth there is often no way to resolve a small object in the Solar System, even in the most powerful of telescopes, since the apparent angular size of the object is smaller than one pixel in the detector. Thus, astronomers measure the amount of light produced by an object as a function of time (the light curve). The time separation of peaks in the light curve gives an estimate of the rotational period of the object. The difference between the maximum and minimum brightnesses (the amplitude of the light curve) can be due to the shape of the object, or to bright and dark areas on its surface. For example, an asymmetrical asteroid's light curve generally has more pronounced peaks, while a more spherical object's light curve will be flatter.[6] This allows astronomers to infer information about the shape and spin (but not size) of asteroids.
Asteroid lightcurve database
Light curve quality code
The Asteroid Lightcurve Database (LCDB) of the Collaborative Asteroid Lightcurve Link (CALL) uses a numeric code to assess the quality of a period solution for minor planet light curves (it does not necessarily assess the actual underlying data). Its quality code parameter U ranges from 0 (incorrect) to 3 (well-defined):[7]
U = 0 → Result later proven incorrect
U = 1 → Result based on fragmentary light curve(s), may be completely wrong.
U = 2 → Result based on less than full coverage. Period may be wrong by 30 percent or ambiguous.
U = 3 → Secure result within the precision given. No ambiguity.
U = n.a. → Not available. Incomplete or inconclusive result.
A trailing plus sign (+) or minus sign (−) is also used to indicate a slightly better or worse quality than the unsigned value.[7]
Light curve of the asteroid 1247 Dysona occulting 4UCAC 174-171272, showing instantaneous disappearance and reappearance. Duration is 6.48 seconds.
The occultation light curve is often characterised as binary, where the light from the star is terminated instantaneously, remains constant for the duration, and is reinstated instantaneously. The duration is equivalent to the length of a chord across the occulting body.
Circumstances where the transitions are not instantaneous are;
when either the occulting or occulted body are double, e.g. a double star or double asteroid, then a step light curve is observed.
when the occulted body is large, e.g. a star like Antares, then the transitions are gradual.
when the occulting body has an atmosphere, e.g. the moon Titan[8]
The observations are typically recorded using video equipment and the disappearance and reappearance timed using a GPS disciplined Video Time Inserter (VTI).
Occultation light curves are archived at the VizieR service.[9]
Periodic dips in a star’s light curve graph could be due to an exoplanet passing in front of the star that it’s orbiting. When an exoplanet passes in front of its star, light from that star is temporarily blocked, resulting in a dip in the star’s light curve. These dips are periodic, as planets periodically orbit a star. Many exoplanets have been discovered via this method, which is known as the Astronomical transit method.
Light curve inversion
Light curve inversion is a mathematical technique used to model the surfaces of rotating objects from their brightness variations. This can be used to effectively image starspots or asteroid surface albedos.[10][11]
Microlensing is a process where relatively small and low-mass astronomical objects cause a brief small increase in the brightness of a more distant object. This is caused by the small relativistic effect as larger gravitational lenses, but allows the detection and analysis of otherwise-invisible stellar and planetary mass objects. The properties of these objects can be inferred from the shape of the lensing light curve. For example, PA-99-N2 is a microlensing event that may have been due to a star in the Andromeda Galaxy that has an exoplanet.[12]
References
^Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007–2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
^Russell, Henry Norris (1912). "On the Determination of the Orbital Elements of Eclipsing Variable Stars. I". Astrophysical Journal. 35: 315. Bibcode:1912ApJ....35..315R. doi:10.1086/141942.
^Kron, Gerald E. (1952). "A Photoelectric Study of the Dwarf M Eclipsing Variable YY Geminorum". Astrophysical Journal. 115: 301. Bibcode:1952ApJ...115..301K. doi:10.1086/145541.
^Wood, P. R.; Sebo, K. M. (1996). "On the pulsation mode of Mira variables: Evidence from the Large Magellanic Cloud". Monthly Notices of the Royal Astronomical Society. 282 (3): 958. Bibcode:1996MNRAS.282..958W. doi:10.1093/mnras/282.3.958.
^"Supernova". Georgia State University – Hyperphysics – Carl Rod Nave. 1998.
^Harris, A. W.; Warner, B. D.; Pravec, P. (2016). "Asteroid Lightcurve Derived Data V16.0". NASA Planetary Data System. 246: EAR-A-5-DDR-DERIVED-LIGHTCURVE-V16.0. Bibcode:2016PDSS..246.....H.
^ ab"Asteroid Lightcurve Data Base (LCDB) – 4.1.2 U (QUALITY) CODE". Collaborative Asteroid Lightcurve Link. 30 October 2011. Retrieved 16 March 2016.
^Harmon, Robert O.; Crews, Lionel J. (2000). "Imaging Stellar Surfaces via Matrix Light-Curve Inversion". The Astronomical Journal. 120 (6): 3274. Bibcode:2000AJ....120.3274H. doi:10.1086/316882.
^Roettenbacher, Rachael M.; Monnier, John D.; Harmon, Robert O.; Barclay, Thomas; Still, Martin (2013). "Imaging Starspot Evolution on Kepler Target KIC 5110407 Using Light-Curve Inversion". The Astrophysical Journal. 767 (1): 60. arXiv:1302.6268. Bibcode:2013ApJ...767...60R. doi:10.1088/0004-637X/767/1/60. S2CID 119221231.
^Haugan, S. V. H. (1996). "Separating Intrinsic and Microlensing Variability Using Parallax Measurements". In Kochanek, C.S.; Hewitt, Jacqueline (eds.). Astrophysical Applications of Gravitational Lensing: Proceedings of the 173rd Symposium of the International Astronomical Union, 9–14 July 1995. Symposium of the International Astronomical Union. Vol. Symposium no. 173. Melbourne; Australia: Kluwer Academic Publishers. p. 277. arXiv:astro-ph/9508112. Bibcode:1996IAUS..173..277H.
External links
The AAVSO online light curve generator 2020-12-21 at the Wayback Machine can plot light curves for thousands of variable stars
have light curves for several transient types, including supernovae
Lightcurves: An Introduction by NASA's Imagine the Universe
DAMIT Database of Asteroid Models from Inversion Techniques
January 10, 2023
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This article is about astronomical graphs of brightness variations For photosynthetic response graphs see Light curve botany In astronomy a light curve is a graph of light intensity of a celestial object or region as a function of time typically with the magnitude of light received on the y axis and with time on the x axis The light is usually in a particular frequency interval or band Light curves can be periodic as in the case of eclipsing binaries Cepheid variables other periodic variables and transiting extrasolar planets or aperiodic like the light curve of a nova a cataclysmic variable star a supernova or a microlensing event or binary as observed during occultation events The study of the light curve together with other observations can yield considerable information about the physical process that produces it or constrain the physical theories about it Light curve of the asteroid 201 Penelope based on images taken on 6 October 2006 at Mount John University Observatory Shows just over one full rotation which lasts 3 7474 hours Contents 1 Variable stars 1 1 Supernovae 2 Planetary astronomy 2 1 Asteroid lightcurve database 2 1 1 Light curve quality code 2 2 Occultation light curves 3 Exoplanet discovery 4 Light curve inversion 5 Microlensing 6 References 7 External linksVariable stars EditMain article Variable star Light curve of d Cephei showing magnitude versus pulsation phase Graphs of the apparent magnitude of a variable star over time are commonly used to visualise and analyse their behaviour Although the categorisation of variable star types is increasingly done from their spectral properties the amplitudes periods and regularity of their brightness changes are still important factors Some types such as Cepheids have extremely regular light curves with exactly the same period amplitude and shape in each cycle Others such as Mira variables have somewhat less regular light curves with large amplitudes of several magnitudes while the semiregular variables are less regular still and have smaller amplitudes 1 The shapes of variable star light curves give valuable information about the underlying physical processes producing the brightness changes For eclipsing variables the shape of the light curve indicates the degree of totality the relative sizes of the stars and their relative surface brightnesses 2 It may also show the eccentricity of the orbit and distortions in the shape of the two stars 3 For pulsating stars the amplitude or period of the pulsations can be related to the luminosity of the star and the light curve shape can be an indicator of the pulsation mode 4 Supernovae Edit Main article Supernova Comparative supernova type light curves Light curves from supernovae can be indicative of the type of supernova Although supernova types are defined on the basis of their spectra each has typical light curve shapes Type I supernovae have light curves with a sharp maximum and gradually decline while Type II supernovae have less sharp maxima Light curves are helpful for classification of faint supernovae and for the determination of sub types For example the type II P for plateau have similar spectra to the type II L linear but are distinguished by a light curve where the decline flattens out for several weeks or months before resuming its fade 5 Planetary astronomy EditMain article Planetary science In planetary science a light curve can be used to derive the rotation period of a minor planet moon or comet nucleus From the Earth there is often no way to resolve a small object in the Solar System even in the most powerful of telescopes since the apparent angular size of the object is smaller than one pixel in the detector Thus astronomers measure the amount of light produced by an object as a function of time the light curve The time separation of peaks in the light curve gives an estimate of the rotational period of the object The difference between the maximum and minimum brightnesses the amplitude of the light curve can be due to the shape of the object or to bright and dark areas on its surface For example an asymmetrical asteroid s light curve generally has more pronounced peaks while a more spherical object s light curve will be flatter 6 This allows astronomers to infer information about the shape and spin but not size of asteroids Asteroid lightcurve database Edit Light curve quality code Edit The Asteroid Lightcurve Database LCDB of the Collaborative Asteroid Lightcurve Link CALL uses a numeric code to assess the quality of a period solution for minor planet light curves it does not necessarily assess the actual underlying data Its quality code parameter U ranges from 0 incorrect to 3 well defined 7 U 0 Result later proven incorrect U 1 Result based on fragmentary light curve s may be completely wrong U 2 Result based on less than full coverage Period may be wrong by 30 percent or ambiguous U 3 Secure result within the precision given No ambiguity U n a Not available Incomplete or inconclusive result A trailing plus sign or minus sign is also used to indicate a slightly better or worse quality than the unsigned value 7 Occultation light curves Edit Further information Occultation Occultations by minor planets Light curve of the asteroid 1247 Dysona occulting 4UCAC 174 171272 showing instantaneous disappearance and reappearance Duration is 6 48 seconds The occultation light curve is often characterised as binary where the light from the star is terminated instantaneously remains constant for the duration and is reinstated instantaneously The duration is equivalent to the length of a chord across the occulting body Circumstances where the transitions are not instantaneous are when either the occulting or occulted body are double e g a double star or double asteroid then a step light curve is observed when the occulted body is large e g a star like Antares then the transitions are gradual when the occulting body has an atmosphere e g the moon Titan 8 The observations are typically recorded using video equipment and the disappearance and reappearance timed using a GPS disciplined Video Time Inserter VTI Occultation light curves are archived at the VizieR service 9 Exoplanet discovery EditPeriodic dips in a star s light curve graph could be due to an exoplanet passing in front of the star that it s orbiting When an exoplanet passes in front of its star light from that star is temporarily blocked resulting in a dip in the star s light curve These dips are periodic as planets periodically orbit a star Many exoplanets have been discovered via this method which is known as the Astronomical transit method Light curve inversion EditLight curve inversion is a mathematical technique used to model the surfaces of rotating objects from their brightness variations This can be used to effectively image starspots or asteroid surface albedos 10 11 Microlensing EditMain article Gravitational microlensing Microlensing is a process where relatively small and low mass astronomical objects cause a brief small increase in the brightness of a more distant object This is caused by the small relativistic effect as larger gravitational lenses but allows the detection and analysis of otherwise invisible stellar and planetary mass objects The properties of these objects can be inferred from the shape of the lensing light curve For example PA 99 N2 is a microlensing event that may have been due to a star in the Andromeda Galaxy that has an exoplanet 12 References Edit Samus N N Durlevich O V et al 2009 VizieR Online Data Catalog General Catalogue of Variable Stars Samus 2007 2013 VizieR On line Data Catalog B GCVS Originally Published in 2009yCat 102025S 1 Bibcode 2009yCat 102025S Russell Henry Norris 1912 On the Determination of the Orbital Elements of Eclipsing Variable Stars I Astrophysical Journal 35 315 Bibcode 1912ApJ 35 315R doi 10 1086 141942 Kron Gerald E 1952 A Photoelectric Study of the Dwarf M Eclipsing Variable YY Geminorum Astrophysical Journal 115 301 Bibcode 1952ApJ 115 301K doi 10 1086 145541 Wood P R Sebo K M 1996 On the pulsation mode of Mira variables Evidence from the Large Magellanic Cloud Monthly Notices of the Royal Astronomical Society 282 3 958 Bibcode 1996MNRAS 282 958W doi 10 1093 mnras 282 3 958 Supernova Georgia State University Hyperphysics Carl Rod Nave 1998 Harris A W Warner B D Pravec P 2016 Asteroid Lightcurve Derived Data V16 0 NASA Planetary Data System 246 EAR A 5 DDR DERIVED LIGHTCURVE V16 0 Bibcode 2016PDSS 246 H a b Asteroid Lightcurve Data Base LCDB 4 1 2 U QUALITY CODE Collaborative Asteroid Lightcurve Link 30 October 2011 Retrieved 16 March 2016 Sicardy B Brahic A Ferrari C Gautiert D Lecacheux J Lellouch E Reques F Arlot J E Colas F 1990 01 25 Probing Titan s atmosphere by stellar occultation Nature 343 6256 350 353 Bibcode 1990Natur 343 350S doi 10 1038 343350a0 ISSN 0028 0836 S2CID 4330667 Dave Herald Derek Breit David Dunham Eric Frappa Dave Gault Tony George Tsutomu Hayamizu Brian Loader Jan Manek 2016 VizieR Online Data Catalog Occultation lights curves Herald 2016 VizieR On line Data Catalog 1 Bibcode 2016yCat 102033H Harmon Robert O Crews Lionel J 2000 Imaging Stellar Surfaces via Matrix Light Curve Inversion The Astronomical Journal 120 6 3274 Bibcode 2000AJ 120 3274H doi 10 1086 316882 Roettenbacher Rachael M Monnier John D Harmon Robert O Barclay Thomas Still Martin 2013 Imaging Starspot Evolution on Kepler Target KIC 5110407 Using Light Curve Inversion The Astrophysical Journal 767 1 60 arXiv 1302 6268 Bibcode 2013ApJ 767 60R doi 10 1088 0004 637X 767 1 60 S2CID 119221231 Haugan S V H 1996 Separating Intrinsic and Microlensing Variability Using Parallax Measurements In Kochanek C S Hewitt Jacqueline eds Astrophysical Applications of Gravitational Lensing Proceedings of the 173rd Symposium of the International Astronomical Union 9 14 July 1995 Symposium of the International Astronomical Union Vol Symposium no 173 Melbourne Australia Kluwer Academic Publishers p 277 arXiv astro ph 9508112 Bibcode 1996IAUS 173 277H External links EditThe AAVSO online light curve generator Archived 2020 12 21 at the Wayback Machine can plot light curves for thousands of variable stars The Open Astronomy Catalogs have light curves for several transient types including supernovae Lightcurves An Introduction by NASA s Imagine the Universe DAMIT Database of Asteroid Models from Inversion Techniques Retrieved from https en wikipedia org w index php title Light curve amp oldid 1127792339, wikipedia, wiki, book, books, library,
