2003A&A...407..573B


Query : 2003A&A...407..573B

2003A&A...407..573B - Astronomy and Astrophysics, volume 407, 573-587 (2003/8-4)

Long-term study of water masers associated with Young Stellar Objects. II. Analysis.

BRAND J., CESARONI R., COMORETTO G., FELLI M., PALAGI F., PALLA F. and VALDETTARO R.

Abstract (from CDS):

We present the analysis of the properties of water maser emission in 14 star forming regions (SFRs), which have been monitored for up to 13 years with a sampling rate of about once every 2-3 months. The 14 regions were chosen to span a range in luminosity Lfir of the associated Young Stellar Object (YSO) between 20L and 1.8x106L. The general scope of the analysis is to investigate the dependence of the overall spectral morphology of the maser emission and its variability on the luminosity of the YSO. We find that higher-luminosity sources tend to be associated with stronger and more stable masers. Higher-luminosity YSOs can excite more emission components over a larger range in velocity, yet the emission that dominates the spectra is at a velocity very near that of the molecular cloud in which the objects are embedded. For Lfir>3x104L the maser emission becomes increasingly structured and more extended in velocity with increasing Lfir. Below this limit the maser emission shows the same variety of morphologies, but without a clear dependence on Lfir and with a smaller velocity extent. Also, for sources with Lfir above this limit, the water maser is always present above the 5σ-level; below it, the typical 5σ detection rate is 75-80%. Although the present sample contains few objects with low YSO luminosity, we can conclude that there must be a lower limit to Lfir (≲430L), below which the associated maser is below the detection level most of the time. These results can be understood in terms of scaled versions of similar SFRs with different YSO luminosities, each with many potential sites of maser amplification, which can be excited provided there is sufficient energy to pump them, i.e. the basic pumping process is identical regardless of the YSO luminosity. In SFRs with lower input energies, the conditions of maser amplification are much closer to the threshold conditions, and consequently more unstable. We find indications that the properties of the maser emission may be determined also by the geometry of the SFR, specifically by the beaming and collimation properties of the outflow driven by the YSO. For individual emission components the presence of velocity gradients seems to be quite common; we find both acceleration and deceleration, with values between 0.02 and 1.8km/s/yr. From the 14 ``bursts'' that we looked at in some detail we derive durations of between 60 and 900-days and flux density increases of between 40% and >1840% (with an absolute maximum of ∼820Jy over 63-days). The ranges found in burst- intensity and -duration are biased by our minimum sampling interval, while the lifetime of the burst is furthermore affected by the fact that bursts of very long duration may not be recognized as such. In addition to the flux density variations in individual emission components, the H2O maser output as a whole is found to exhibit a periodic long-term variation in several sources. This may be a consequence of periodic variations in the wind/jets from the exciting YSO.

Abstract Copyright:

Journal keyword(s): masers - stars: formation - radio lines: ISM

CDS comments: Table 1 : designations 'NN' in column 1 not in Simbad. In reflist, Valdettaro A&A.383.244 : 2001 is a misprint for 2002.

Simbad objects: 34

goto Full paper

goto View the references in ADS

Number of rows : 34
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
#notes
1 [SHK2000] 00494+5617 Mas 00 52.3 +56 33           ~ 3 0
2 NGC 281 HII 00 52 25.1 +56 33 54           ~ 241 1
3 [PCC93] 43 Mas 03 27 38.1 +30 12 59           ~ 4 0
4 NAME LDN 1455 IRS 1 cor 03 27 39.08 +30 13 03.1           ~ 160 0
5 [PGS81] IRS 2 Y*O 05 47 05.388 +00 21 50.05           ~ 33 0
6 NGC 2071 RNe 05 47 10 +00 18.0           ~ 644 1
7 NAME Mon R2 HII 06 07 47.58 -06 22 42.6           ~ 736 2
8 NAME Mon R2 IRS 3 Y*O 06 07 47.8 -06 22 55           ~ 141 0
9 [PCC93] 92 Mas 06 07 48.0 -06 23 04           ~ 4 0
10 Caswell H2O 196.46-01.68 Mas 06 14 36.5 +13 49 33           ~ 6 0
11 IRAS 06117+1350 HII 06 14 37 +13 49.6           ~ 55 0
12 IRAS 18449-0158 HII 18 47 35.6 -01 55 26           ~ 24 0
13 Caswell H2O 030.81-00.06 Mas 18 47 47.0 -01 54 35           ~ 10 0
14 Caswell OH 032.74-00.07 Mas 18 51 20.0 -00 11 51           ~ 11 0
15 IRAS 18487-0015 IR 18 51 20.6 -00 11 46           ~ 19 0
16 GAL 032.74-00.08 reg 18 51 21.95 -00 12 08.7           ~ 4 0
17 RAFGL 2271 SFR 18 53 18.54 +01 14 57.9           ~ 503 0
18 OH 034.26+00.15 Mas 18 53 18.68 +01 15 00.3           ~ 31 0
19 SNR G034.6-00.5 SNR 18 56 10.650 +01 13 21.30           ~ 960 2
20 GAL 035.2-00.74 cor 18 58 13.00 +01 40 36.0           ~ 169 0
21 OH 035.2-00.7 Mas 18 58 13.0517 +01 40 35.674           ~ 43 0
22 IRAS 18556+0136 mul 18 58 13.1 +01 40 35           ~ 139 0
23 MSX6C G059.7831+00.0648 Y*O 19 43 11.2464 +23 44 03.270           ~ 137 0
24 IRAS 19410+2336 SFR 19 43 11.5 +23 44 06           ~ 154 0
25 SH 2-128 HII 21 32 09.9 +55 52 53           ~ 168 1
26 NAME S128(H20) Mas 21 32 11.44 +55 53 54.7           ~ 18 0
27 [HLB98] Onsala 156 Mas 21 43 00.2 +66 03 26           ~ 5 0
28 NAME NGC 7129 FIR 2 IR 21 44 01.5 +66 03 40           ~ 97 0
29 SH 2-140 OpC 22 19 07.8 +63 17 07           ~ 656 2
30 IRAS 22176+6303 Y*O 22 19 18.23 +63 18 47.5           ~ 594 0
31 NAME SH 2-140 IRS 1 Y*O 22 19 18.277 +63 18 45.82           ~ 196 0
32 LDN 1204G cor 22 19 19.1 +63 18 51           ~ 10 0
33 [XT92] 9 Mas 22 21.4 +63 51           ~ 7 0
34 LDN 1204A HII 22 21 26.68 +63 51 38.2           ~ 108 0

To bookmark this query, right click on this link: simbad:objects in 2003A&A...407..573B and select 'bookmark this link' or equivalent in the popup menu