2007A&A...468..501A


C.D.S. - SIMBAD4 rel 1.7 - 2020.07.06CEST20:52:45

2007A&A...468..501A - Astronomy and Astrophysics, volume 468, 501-514 (2007/6-3)

Unbinned maximum-likelihood estimators for low-count data. Applications to faint X-ray spectra in the Taurus molecular cloud.

ARZNER K., GUEDEL M., BRIGGS K., TELLESCHI A., SCHMIDT M., AUDARD M., SCELSI L. and FRANCIOSINI E.

Abstract (from CDS):

Traditional binned statistics such as χ2 suffer from information loss and arbitrariness of the binning procedure, which is especially important at low count rates as encountered in the XMM-Newton Extended Survey of the Taurus Molecular Cloud (XEST). We point out that the underlying statistical quantity (the log likelihood L) does not require any binning beyond the one implied by instrumental readout channels, and we propose to use it for low-count data. The performance of L in the model classification and point estimation problems is explored by Monte-Carlo simulations of Chandra and XMM-Newton X-ray spectra, and is compared to the performances of the binned Poisson statistic (C), Pearson's χ2 and Neyman's χ2N, the Kolmogorov-Smirnov, and Kuiper's statistics. It is found that the unbinned log likelihood L performs best with regard to the expected chi-square distance between true and estimated spectra, the chance of a successful identification among discrete candidate models, the area under the receiver-operator curve of reduced (two-model) binary classification problems, and generally also with regard to the mean square errors of individual spectrum parameters. The χ22N) statistics should only be used if more than 10 (15) predicted counts per bin are available. From the practical point of view, the computational cost of evaluating L is smaller than for any of the alternative methods if the forward model is specified in terms of a Poisson intensity and normalization is a free parameter. The maximum-L method is applied to 14 XEST observations, and confidence regions are discussed. The unbinned results are compared to binned XSPEC results, and found to generally agree, with exceptions explained by instability under re-binning and by background fine structures. In particular, HO Tau is found by the unbinned method to be rather cool (kT∼0.2keV), which may be a sign of shock emission. The maximum-L method has no lower limit on the available counts, and allows to treat weak sources which are beyond the means of binned methods.

Abstract Copyright:

Journal keyword(s): methods: statistical - X-rays: stars - stars: formation

Simbad objects: 18

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Number of rows : 18

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 NAME IRAS 04108+2803B Y*O 04 13 54.71688 +28 11 32.8992           K0-M3 36 0
2 [BCG93] 1 TT* 04 14 17.6094853639 +28 06 09.650035718 18.04         M4.5 73 0
3 2MASS J04181710+2828419 TT* 04 18 17.1091861192 +28 28 41.921033525     22.175     M6.4 74 0
4 V* DD Tau Or* 04 18 31.1271804823 +28 16 29.158626278 15.94 15.49 14.10 13.76   M3.5e+M3.5e 177 0
5 IRAS 04154+2823 Y*O 04 18 32.0460600618 +28 31 14.990027099           M2.5 59 0
6 2MASS J04190110+2819420 TT* 04 19 01.1041061433 +28 19 42.084605479           M5.9 54 0
7 2MASS J04270266+2605304 Y*O 04 27 02.66593 +26 05 30.3790           ~ 135 0
8 V* DG Tau Or* 04 27 04.6913654419 +26 06 16.041555299 13.57 13.97 10.50 12.28   K6Ve 923 1
9 V* GV Tau TT* 04 29 23.7314759229 +24 33 00.216016292 19.20         K7 271 2
10 Haro 6-13 Or* 04 32 15.4177438039 +24 28 59.580866027 19.22   17.7     M0 181 1
11 V* HO Tau Or* 04 35 20.2103777721 +22 32 14.557063236     15.20     M0.5 106 0
12 IRAS 04325+2402 Y*O 04 35 35.39160 +24 08 19.4244           ~ 150 0
13 V* GN Tau Or* 04 39 20.922216 +25 45 02.02608 17.22     13.85   M2.5 85 0
14 IRAS 04365+2535 Y*O 04 39 35.19360 +25 41 44.7252           ~ 237 0
15 IRAS 0437+257P08 TT? 04 39 55.7451364657 +25 45 01.943057594           B5 159 1
16 NAME Taurus Complex SFR 04 41.0 +25 52           ~ 3478 0
17 V* DP Tau Or* 04 42 37.6996387891 +25 15 36.992730557 15.84 15.2 13.70 14.42   M0.8 154 1
18 V* TW Hya TT* 11 01 51.9054298616 -34 42 17.031550898   11.94 10.50 10.626 9.18 K6Ve 1532 1

    Equat.    Gal    SGal    Ecl

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2020.07.06-20:52:45

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