2000ApJ...540..255P


C.D.S. - SIMBAD4 rel 1.7 - 2020.02.27CET21:06:55

2000ApJ...540..255P - Astrophys. J., 540, 255-270 (2000/September-1)

Accelerating star formation in clusters and associations.

PALLA F. and STAHLER S.W.

Abstract (from CDS):

We use our own, recently developed pre-main-sequence evolutionary tracks to investigate the star formation histories of relatively nearby associations and clusters. We first employ published luminosities and effective temperatures to place the known members of each region in the H-R diagram. We then construct age histograms detailing that region's history. The groups studied include Taurus-Auriga, Lupus, Chamaeleon, ρ Ophiuchi, Upper Scorpius, IC 348, and NGC 2264. This study is the first to analyze a large number of star-forming regions with the same set of theoretical tracks.

Our investigation corroborates and extends our previous results on the Orion Nebula Cluster. In all cases, we find that star formation began at a relatively low level some 107 yr in the past and has more recently undergone a steep acceleration. This acceleration, which lasts several million years, is usually continuing through the present epoch. The one clear exception is the OB association Upper Scorpius, where the formation rate climbed upward, peaked, and has now died off. Significantly, this is also the only region of our list that has been largely stripped of molecular gas.

The acceleration represents a true physical phenomenon that cannot be explained away by incompleteness of the samples; nor is the pattern of stellar births significantly affected by observational errors or the presence of unresolved binaries. We speculate that increasing star formation activity arises from contraction of the parent cloud. Despite the short timescale for acceleration, the cloud is likely to evolve quasi-statically. Star formation itself appears to be a critical phenomenon, occurring only in locations exceeding some threshold density. The cloud's contraction must reverse itself, and the remnant gas dissipate, in less than 107 yr, even for aggregates containing no massive stars. In this case, molecular outflows from the stars themselves presumably accomplish the task, but the actual dispersal mechanism is still unclear.


Abstract Copyright:

Journal keyword(s): open clusters and associations: individual (Chamaeleon, IC 348, Lupus, NGC 2264, Orion Nebula Cluster, ρ Ophiuchi, Taurus-Auriga, Upper Scorpius) - Stars: Evolution - Stars: Formation - Stars: Pre-Main-Sequence

CDS comments: p. 264, 265 : W178 = NGC 2264 178

Simbad objects: 44

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Number of rows : 44

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 NGC 1333 SFR 03 28 55 +31 22.2   10.9       ~ 1200 1
2 NAME Perseus Cloud SFR 03 35.0 +31 13           ~ 1027 0
3 Ass Per OB 2 As* 03 42.2 +33 26           ~ 304 0
4 IC 348 OpC 03 44 34 +32 09.8           ~ 1212 1
5 HD 281159 Y*? 03 44 34.197 +32 09 46.27 9.19 9.21 8.53   7.850 B5V 201 2
6 LDN 1495E Cl* 04 13 30.7 +28 19 15           ~ 31 0
7 IRAS 04191+1523 Y*O 04 22 00.439 +15 30 21.21           ~ 183 0
8 NAME Tau-Aur Region SFR 04 30 +25.0           ~ 1193 1
9 LDN 1527 DNe 04 39 53 +25 45.0           ~ 478 0
10 NAME Orion Nebula Cluster OpC 05 35.0 -05 29           ~ 1932 1
11 NAME Trapezium Cluster As* 05 35 16.5 -05 23 14           ~ 1445 1
12 M 42 HII 05 35 17.3 -05 23 28           ~ 3687 0
13 NAME Ori A MoC 05 38 -07.1           ~ 2639 0
14 NAME ORI MOL CLOUD MoC 05 56 -01.8           ~ 831 1
15 NGC 2264 OpC 06 40 58 +09 53.7     3.9     ~ 1565 1
16 * 15 Mon Be* 06 40 58.65963 +09 53 44.7229 3.360 4.400 4.640   4.88 O7V+B1.5/2V 743 0
17 NAME Cone Nebula DNe 06 41.1 +09 53           ~ 74 1
18 HD 47887 pr* 06 41 09.5990835362 +09 27 57.540646250 6.01 6.96 7.14   7.40 B2III: 98 0
19 NAME Cha I MoC 11 06 48 -77 18.0           ~ 947 1
20 NAME Cha T Association As* 11 08 -77.0           ~ 40 1
21 NAME Lower Centaurus Crux As* 12 19 -57.1           ~ 340 1
22 IRAS 12340-7958 * 12 37 39.7466355997 -80 15 13.713429632   16.11 14.39 13.63 9.81 ~ 101 0
23 NAME Cha III MoC 12 37.8 -80 15           ~ 122 2
24 V* DK Cha Or* 12 53 17.2028372976 -77 07 10.727661977           F0 132 0
25 NAME Cha II MoC 12 54 -77.2           ~ 295 0
26 NAME Upper Centaurus Lupus As* 15 24 -41.9           ~ 346 1
27 NAME Lupus I Cld 15 43 02.1 -34 09 06           ~ 217 0
28 NAME Lup II MoC 15 57 08 -37 47.1           ~ 90 1
29 NAME Lup Cloud SFR 16 03 -38.1           ~ 495 0
30 NAME Lupus IV MoC 16 03 12.4 -42 07 43           ~ 123 0
31 NAME Lupus III SFR 16 09.6 -39 03           ~ 266 0
32 NAME Upper Sco Association As* 16 12 -23.4           ~ 977 1
33 NAME ASSOC II SCO As* 16 15 -24.2           ~ 1093 1
34 NAME rho Oph Complex reg 16 25 -23.5           ~ 76 1
35 * rho Oph ** 16 25 35.11766 -23 26 49.8150 4.30 4.85 4.63 4.27 3.96 B2IV+B2V 596 2
36 NAME rho Oph A Cloud MoC 16 26 26.4 -24 22 33           ~ 237 1
37 NAME rho Oph C Cloud MoC 16 26 53.1 -24 32 31           ~ 54 0
38 * chi Oph Be* 16 27 01.4349892 -18 27 22.493784 3.95 4.71 4.43 3.97 3.73 B2Vne 563 0
39 NAME rho Oph E MoC 16 27 02.0 -24 38 31           ~ 54 0
40 NAME rho Oph B Cloud MoC 16 27 11 -24 28.5           ~ 64 1
41 NAME rho Oph F MoC 16 27 37.3 -24 42 28           ~ 56 0
42 NAME Ophiuchus Molecular Cloud SFR 16 28 06 -24 32.5           ~ 2972 0
43 NAME Ophiuchus D MoC 16 28 29.2 -24 18 25           ~ 102 0
44 LDN 1689 DNe 16 32 22.5 -24 28 29           ~ 106 0

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2020.02.27-21:06:55

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