Magellanic Clouds

1
Magellanic Clouds

• Visible only from the far south
• Sizes larger than visual
• Lots of blue stars
• Nearest large neighbors

2
Why study?

• Little dust towards them
• (though they have dust in them)
• Large star formation regions
• Large samples of stars
• Proximity - How close?
• Distances studied since 1900s
• Cepheids, RR Lyrae, Novae, OB Stars, Cluster
  isochrones, SN1987A, ..
• LMC m-M18.45 (49 kpc 50 kpc)
• SMC m-M18.9 (60 kpc)

3
Properties

• SMC
• Mass 2 billion M?
• H I mass 30
• Molecular gas 1
• Fe/H-0.6 (1/4 solar)
• Disk?not seen, but H I deep
• H II regions a few large ones
• Cluster 2000
• Bar structure mainly blue stars
• Halo stellar probably
• Halo gas x-ray

• LMC
• Mass 20 billion M?
• H I mass lt 8 total
• Molecular gas 1
• Fe/H -0.3 (1/2 solar)
• Disk? young
• H II regions many
• Clusters 6500
• Bar structure red, H II, star formation
• Halo stellar probably
• Halo gas x-ray

4
Structures

• LMC
• Disk nearly face on
• Bar
• No arms, but rotates

5
Star Density map
H I
6

• SMC
• No real structure
• Strong projection angle?
• N-S/E-W/Depth ratios 124

7
Cluster

• Easy to observe
• Provide information on age/Fe/H/distance
• NOT LIKE MILKY WAY CLUSTERS!
• Old clusters gt10 Gyrs
• Content RR Lyrae, old red stars
• LMC 8-14?, Fe/H -1.4 to -2.1
• SMC 1, Fe/H-1.84
• Very few REAL globular clusters!

8

• Few Gyrs old
• Content Blue(!) GC, fewer red stars, RR Lyrae
• More in SMC than LMC
• Fe/H-0.6 (LMC)
• -0.9 (SMC)
• lt100 Myrs old
• Content Star formation, young stars, Cepheids
• LMC Super associations, Fe/H -0.2 to 0
• SMC few associations, Fe/H -0.2 to 0

9
Whats up with the clusters?

• GC
• Numbers not unusual for mass of galaxy
• Location not normal aligned with the disks
• Intermediate age clusters
• Young Globular clusters
• Structure of MW Globular clusters
• Blue stars!
• Recently formed? How?

10

• Youngest clusters
• Super associations
• Massive regions of star formation
• Many young stars (OB, WR)
• Evolved massive stars (B-G Supergiants)
• Cepheids
• 8 in LMC, 1 in SMC
• Supergiant Stromgren spheres, R300-700 pc

11
(No Transcript)
12
(No Transcript)
13
Star Formation Histories

• Not steady
• Initially after formation (gt10 Gyrs ago)
• Quiet period
• Lots 5 Gyrs ago
• Quiet period
• Lots recently (lt1 Gyr ago)
• SMC follows pattern of LMC, but lesser

14
Tarantula Nebula

• R 300 pc
• Few million M?

15
Cluster30 Doradus
16
(No Transcript)
17
Red x-ray Green H II emission Blue UV
18
(No Transcript)
19
(No Transcript)
20
R136 many more stars.
21
SN1987A

• Feb. 1987
• Type I - massive star
• First naked eye SN since 1604
• Distance measurement

22
Histories of the MCs

• Common history common environment
• H I envelope and bridge
• Gravitationally bound
• To each other
• To the MW
• Magellanic Stream
• 2 Gyrs old?

23
(No Transcript)
24
(No Transcript)
25
(No Transcript)
26
(No Transcript)
27
MACHO studies

• OGLE
• 7 million stars in LMC
• 2 million stars in SMC
• Discoveries
• Cepheids (1300, 2050 in LMC,SMC)
• RR Lyrae (7600, 570)
• And many other variables (20,000 in each)

28
(No Transcript)