Populasi Bintang & Distribusi Bintang

1. PopulasiBintang &DistribusiBintang AS-3220 FisikaGalaksi

2. Outline • Pendahuluan review astrofisika • Sejarahsingkatstudipopulasibintang di Galaksi • PopulasiBintang di Galaksi • CacahBintang (Star counts) • Aliranbintang (Star streams) • Topikkhusus Galactic Archaeology

3. Tujuandanprasyarat Tujuan : • Memahami korelasi antara berbagaipropertigalaksi denganmenggunakan prinsip-prinsip fisika, untukmemahamipembentukandan evolusi galaksi • Memahami secara rinci struktur Bima Sakti (distribusibintang dan MAB, metalisitas,kinematika bintang, dan distribusiusia) Prasyarat : • Mengerti berbagai besaran astrofisika bintang seperti umur, massa, komposisi kimia, temperatur efektif, kelas spektrum, tahap-tahap evolusi bintang

4. Review Astrofisika • Umum : modulus jarak, magnitudomutlak, Luminositasbolometrikdanfungsi Planck  Fotometri • Tipebintang: deretutama (dwarf), kataiputih, cabanghorisontal, raksasa, super-raksasa, sub-raksasa, subdwarfdll. • Propertibintang: massa, temperaturefektif, kelasspektrum, umur, metalisitas

5. Review Astrofisika Apa yang kitaukur? Intensitasradiasi : I, , , t, p • I - energi (ataujumlahfoton) / waktu/ Hz / solid angle •  - darisinar gamma hingga radio, bergantungpadaresolusi spektroskopi, fotometri pita sempit (narrow-band photometry) danfotometri pita lebar (broad-band photometry) •  ,  - arah(posisipadabidanglangit); resolusioptispadaarahtersebutmembagisumbermenjaditak-terpisahkan (unresolved, sumbertitik) dan resolved; interferometry, adaptive optics,... • t - static vs. variable universe, sampling rate,... • p - polarization

6. Sloan Digital Sky Survey (SDSS) and SEGUE: Sloan Extension for Galactic Understanding and Exploration • SDSS is the most ambitious astronomy project yet undertaken • Obtain accurately calibrated imaging of 10,000 square degrees of (northern) sky, in five filters (ugriz) • Obtain moderate-resolution spectroscopy for • 1,000,000 galaxies • 100,000 quasars • Has been fully operational since ~ Jan 2000 • Completed (or nearly so) its primary imaging mission in July 2005, first extension through July 2008, second extension through July 2014

7. The ARC 2.5m Telescope ARC 2.5m SDSS Telescope (3 deg FOV)

8. The SDSS Imaging Camera The actual camera and a block diagram of the CCD layout

9. Fotometri bintang

10. 1' (l,b) = (50, -15) Star Density = 50,000 per sq. deg with g<23

12. Two spectrographs, with spectral coverage from 3800 – 9000 A The SDSS Spectrograph(s)

13. A Cartoon Version

14. The SDSS Spectrograph Plug Plate Identification of targets on the sky A prepped and drilled plate

15. AnalisaSpektrumBintang • Appearance of stellar spectra can be influenced by many physical phenomena – some have dramatic affect, some more subtle, some difficult to notice even with high quality, high-dispersion spectra • Most important ones for understanding of the nature of a given star are the principle stellar atmospheric parameters • Teff = Effective Temperature (K) • log g = Stellar surface gravity (dex) • [Fe/H] = Stellar metallicity (dex) • [X/Fe] = Other elemental abundance ratios

17. The appearance of stellar spectra is mostly affected by their temperature, in particular with different species, and ionization states being available for different Teffs. Wide variations in surface gravity yield visually detectable differences in spectra. Abundance variations often more subtle, but in extreme cases, visually detectable as well.

18. SEGUE Sample Spectra – Horizontal-Branch Stars

19. SEGUE Sample Spectra – F Turnoff Stars

20. SEGUE Sample Spectra – G Dwarf Stars

21. Comparing Spectra

22. Diagram Hertzsprung-Russel

23. Radius

25. Sejarahsingkatstudipopulasibintang di Galaksi The history of understanding the stellar populations of the Milky Way provides an illustration of the above process. In the history provided here, the symbol  = "A correlation of properties" 1. At the beginning of the 20th century, Milky Way studies was essentially "cosmology", since at the time it was not appreciated that there were galaxies outside our own."Sidereal Universe" = Milky Way.Until 1920: Curtis-Shapley Debate. 2. Early 20th century stellar population studies concerned with taxonomy: • e.g., groups of stars based on: • velocities (proper motions, radial velocities) • stellar types: e.g., colors, brightness, variability, spectral type • location: e.g., in spiral arms, in clusters/associations, in bulge • Kapteyn, Jeans, Smart, Stromberg, Oort, Lindblad... •  "Star streams": kinematical subsystems  Galactic position/structural shape

26. Early work by Lindblad (1936, MNRAS, 97, 15) on the understanding of stars of different types in different orbits, characterized by differences in conserved quantities (``integrals of motion"), energy (I1) and angular momentum (I2).

27. Sejarahsingkatstudipopulasibintang di Galaksi 3. Stellar evolution theoretical advances in 1950's - understanding of chemistry and ages of stars • Allows age dating of clusters, CMD's (Sandage & Schwarzschild 1952) ages  CMD types (Of course, earlier in the 20th century, the Hertsprung-Russell Diagram (HR Diagram) was invented; showed that stars do not occupy random distributions of luminosity and spectral type/temperature/color.)

28. Sandage & Schwarzschild's (1952, ApJ, 116, 463) development of an understanding of the positions of stars in a cluster color-magnirude diagram on the basis of stellar evolution.

29. Understanding nucleosynthesis in stars (e.g., Burbidge, Burbidge, Fowler, Hoyle 1957) -- notion of chemical enrichment with time

30. 4. Connections between structure, kinematics, age, chemistry, stellar (CMD) types A. Chamberlain & Aller (1951) - enrichment levels "written" in spectra chemistry  gives relative age • Note concept of an Age-Metallacity Relation (AMR) • Ultraviolet excess as simple way to get relative metallicities of stars through photometry, rather than spectroscopy - metal lines are crowded toward UV part of spectrum. (Sandage, Eggen: 1950s, 1960s) B. Sandage & Walker (1955) - weak-lined Milky Way field stars look like globular cluster stars (via Ultraviolet Excess)  cluster stars  calibrate field star age-dating  chemistry (e.g., UV excess) absolute ages  Develop a general AMR for Milky Way field stars. C. Baade (1944), Oort (1926) First sweeping collectivization of ``stellar populations"  CMD types  structural components

31. First sweeping collectivization of “stellar population” properties CMD types  structural components The Andromeda system M31, M32 and N205.

32. Baade's famous plate, reproduced from Majewski (ed.), Galaxy Evolution: The Milky Way Perspective, ASP Conf. Ser. 49.

33. High contrast zoom of previous image to show the incipient resolution of the "Baade sheet". Baade's famous plate, reproduced from Majewski (ed.), Galaxy Evolution: The Milky Way Perspective, ASP Conf. Ser. 49.

34. Baade's definition of populations based on CMD type.

35.  structural components <--> kinematical groups • POP I = Disks = "slow-moving" (OB stars, open clusters) • POP II = Bulges, Halos = "fast-moving" (globular clusters, "cluster variables") Aside: Note potentially confusing, historical nomenclature that "slow-moving" and "fast-moving" (and "low" and "high velocity") here are stated with respect to the Sun, which is itself rotating quickly about the Galaxy. Thus, the true rotational velocities of the stars are actually pretty much the opposite of these labels... Note also:  extragalactic systems <--> analogs to Milky Way populations D. Nancy Roman (1954), in a spectroscopic study of high and low velocity stars, makes final ties metal-weak -- high velocity metal-rich -- low velocity  age-metallicity groups <--> structure-kinematical groups E. 1957 Vatican Conference on Stellar Populations: "Meeting of the world's great astronomical minds" to piece together and organize understanding of Galactic populations.

36. Baade's Population II: • K giants brighter than Pop I (now known to be an abundance effect). • No red and blue supergiants (now known to be an age effect). • Has short period, cluster Cepheids (i.e. RR Lyrae stars -- now known to be an age/metallicity effect). • "high velocity stars (w.r.t. Sun)" (kinematics). • subdwarfs (now known to be an abundance effect). • weak-lined stars (now known to be an abundance effect). • globular clusters • dE, Sa galaxies (central parts anyway; location). • outer Milky Way and bulge (location). • "Pop II can be found without associated Pop I".

37. Baade's Population I: • Open clusters (already known to be connected to slow moving stars). • OB stars (now known as an age effect). • solar neighborhood stars (location). • "slow moving stars (w.r.t. Sun)": (kinematics). • strong lines stars (abundance). • "only seen with Population II stars associated" (e.g., Milky Way, Spirals, Magellanic Cloud clusters).

38. halo disk bulge Spiral Galaxy

39. Disk Component: Bintangdenganberbagai umurdanbanyakawan gas Spheroidal Component: bulge & halo, bintang-bintangtua, dansedikitawan gas

40. Disk Component: Bintangdenganberbagai umurdanbanyakawan gas Spheroidal Component: bulge & halo, bintang-bintangtua, dansedikitawan gas

41. Disk Component: Bintangdenganberbagai umurdanbanyakawan gas Warnabiru-putihmengindikasikanadanya proses pembentukanbintang Spheroidal Component: bulge & halo, bintang-bintangtua, dansedikitawan gas Warnamerah-kuningmengindikasikanbintang-bintangtua

42. Disk Component: Bintangdenganberbagai umurdanbanyakawan gas Warnabiru-putihmengindikasikanadanya proses pembentukanbintang Spheroidal Component: bulge & halo, bintang-bintangtua, dansedikitawan gas Warnamerah-kuningmengindikasikanbintang-bintangtua

43. Subdivide/refine Baade's broad groupings: Summary tables from the 1957 Vatican Conference proceedings. This book makes great reading, because all of the conversations of participants have been preserved and recorded in the proceedings. Note that the ages listed in the table are based on well outdated stellar evolution models, and are too small by about a factor of two.

44. F. A “conventional, modern view of the primary Galactic stellar populations and their spatial (density law), chemical, and kinematical properties. Though it should be kept in mind that this conventional picture is still debated.

45. Note the difference between the luminous stellar halo, and the dark matter halo postulated to exist and in which the luminous matter is embedded. Another view of the Milky Way and its populations. From Buser (2000, Science, 287, 5450, 69). His caption: Schematic view of the major components that make up the Galaxy's overall structure, shown in a cross section perpendicular to the plane of rotation and going through the sun and the Galactic center. From the observer's vantage point at the sun's position, the directions to the North (NGP) and South (SGP) Galactic Poles are particularly suitable for studying the layered structure and other properties of the stellar disks and halo, whereas the concentration of gas and dust in the extreme disk severely obstructs observations of the distant bulge at visual-optical wavelengths. The central parts of the Galaxy are better accessible through longer wavelength infrared and radio observations.

46. Populasi Bintang di Galaksi • Populasi Bintang : kumpulan bintang dengan properti (karakteristik) yang sama • Parameter penting yang menyatakan properti yang sama adalah umur (bukan massa bintang ). • Beberapa parameter lain yang menunjukkan properti yang sama adalah : • Komposisi kimia awal (metalisitas) • Fungsi massa awal (IMF), fraksi bintang ganda • Kinematika • Jarak • Distribusi ruang • Asal-usul, sejarah pembentukan bintang • Sebuah populasi dimana semua bintangnya memiliki umur dan metalisitas yang sama disebut : simple stellar population (SSP). Contoh : open cluster

47. Asumsi • Sebuah galaksi terdiri dari berbagai populasi (bintang dengan berbagai umur dan metalisitas, gas dan molekul antar bintang) • Galaksi = Nipopulasii= gabungan (composite) populasi • Populasi = NiSSPi= superposisi dari berbagai SSP • Contoh Bima Sakti : • Komponen Galaksi dengan berbagai populasi yang terpisah seperti bulge, disk dan halo • Setiap komponen terdiri dari gabungan berbagai macam SSP

48. Parameter-parameter yang digunakan untuk menjelaskan properti dari populasi bintang : • Fungsi massa awal (Initial Mass Function – IMF) : IMF=IMF(x,t) • Kelimpahan spesies atom Xj : X=X(x,t,X1,X2,X3,...) • Laju pembentukan bintang (Star Formation Rate – SFR): SFR=SFR(x,t) • Distrubusi bintang (dan gas) pada ruang fase: f = f (x,v,t) • Evolusi terhadap waktu : chemo-dynamical models

49. Komponen Utama • Beberapa contoh gabungan populasi komponen utama dalam Bima Sakti kita adalah : halo, disk dan bulge. • Masing-masing kelompok di atas merupakan kompleks bintang-bintang dan materi antar bintang, tapi dengan sifat global yang berbeda / distribusi kimia / umur / kinematika dari satu sama lain. • Perbedaan ini mungkin berhubungan dengan campuran yang berbeda dari SSP. • Semakin kecil basis set (n, mn), semakin mudah adalah populasi komposit (dan, akhirnya, sejarah Galactic) untuk diungkap • Mengidentifikasi SSPS individu mungkin sulit di galaksi yang kompleks, tapi, mungkin untuk SSP yang dirangkai dalam pola agak sederhana. .

50. (misalkan pembentukan bintang pada piringan dengan memperkaya serangkaian pembentukan SSP disertai meningkatnya kecepatan rotasi terhadap pusat). . . yang membentuk populasi komponen utama dari sebuah galaksiIni adalah satu tujuan dari studi populasi bintang.Kita berharap untuk menyederhanakan apa yang mungkin menjadi masalah yang rumit untuk menemukan salah satu pola dalam Populasi Komponen Utama.