Determination of confidence limits for experiments with low numbers of counts

Kraft, Ralph; Burrows, D. N.; Nousek, J. A.

doi:10.1086/170124

Cited by 477 publications

(558 citation statements)

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“…Finally, count rates were obtained using the exposure time at the source position extracted from the exposure map. We estimated a 95% confidence upper limit for the count rate at the position of "J" in the 2003 Dec. observation using the algorithm of Kraft et al (1991). In Table 2 we summarize the relevant Xray parameters of the Z CMa binary and the source "J" identified with the jet.…”

Section: Data Analysis and Resultsmentioning

confidence: 99%

The X-ray emission from Z Canis Majoris during an FUor-like outburst and the detection of its X-ray jet

Stelzer¹,

Hubrig

Orlando³

et al. 2009

A&A

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Accretion shocks have been recognized as an important X-ray emission mechanism for pre-main sequence stars, and yet the X-ray properties of FUor outbursts, events that are caused by violent accretion, have been given little attention. We observed the FUor object Z CMa during optical outburst and quiescence with Chandra. No significant changes in X-ray brightness and spectral shape were found, suggesting that the X-ray emission is coronal. The binary nature of Z CMa makes the origin of the X-ray source ambiguous. However, the moderate hydrogen column density derived from our data makes it unlikely that the embedded primary star is the Xray source. The secondary star, which is the FUor object, is thus responsible for both the X-ray emission and the ongoing accretion outburst, which seem, however, to be unrelated phenomena. The secondary is also known to drive a large outflow and jet, which we detect here for the first time in X-rays. The distance of the X-ray emitting outflow source to the central star is greater than in jets of low-mass stars.

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Section: Data Analysis and Resultsmentioning

confidence: 99%

The X-ray emission from Z Canis Majoris during an FUor-like outburst and the detection of its X-ray jet

Stelzer¹,

Hubrig

Orlando³

et al. 2009

A&A

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“…The fluxes were determined by integrating the line over 6.4 Å centered on the doublet; the integration limits were set by visual examination of the individual spectra. The significance of these detections can be estimated from the off-source background in the images, as discussed by Kraft, Burrows, & Nousek (1991); see also Babu & Feigelson (1996). The image of each STIS spectrum shows a clear variation in the background along the dispersion direction, likely due to scattered light from the strong Lya airglow present.…”

Section: Resultsmentioning

confidence: 99%

“…Using the Bayesian method described by Kraft et al (1991), we have estimated the 68.3% confidence limits. 3 The flux confidence limits for each spectrum are reported in Table 1.…”

Section: Resultsmentioning

confidence: 99%

Transition Region Emission from Very Low Mass Stars

Hawley

Johns–Krull

2003

ApJ

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We present results from our Cycle 10 Hubble Space Telescope (HST) program to search for transition region emission in very low mass main-sequence stars in the spectral range M7-M9. Our program is aimed at (1) detecting emission and (2) distinguishing between flaring and quiescent origin for the emission. We have obtained HST/Space Telescope Imaging Spectrograph time series observations of three active, very low mass stars (VB 8, VB 10, and LHS 2065), which show persistent activity in transition region lines including Si iv, C iv, and He ii. Emission in transition region lines appears to be variable between exposures but is always observed. A strong flare was also observed in one 10 minute exposure on VB 10. Our results indicate that active, very low mass stars maintain a persistent quiescent chromosphere and transition region that is similar to those observed in active earlier type M dwarfs, in contrast to suggestions that these low-mass main-sequence stars exhibit only relatively strong flares and no quiescent emission.

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“…In the source region we then count the number of photons recorded in the various energy bands and detectors, listed in column "s" in Table 2. Source counts are given with 1σ confidence limits for low count numbers according to Kraft et al (1991); for a detailed discussion, see Ayres (2004). The scaled background counts (denoted "b") were taken from areas much larger than the source region, and thus the error on the background is dominated by statistical fluctuations.…”

Section: Xmm-newton Data Analysismentioning

confidence: 99%

51 Pegasi – a planet-bearing Maunder minimum candidate

Poppenhäger¹,

Robrade²,

Schmitt³

et al. 2009

A&A

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We observed 51 Peg, the first detected planet-bearing star, in a 55 ks XMM-Newton pointing and in 5 ks pointings each with Chandra HRC-I and ACIS-S. The star has a very low count rate in the XMM observation, but is clearly visible in the Chandra images due to the detectors' different sensitivity at low X-ray energies. This allows a temperature estimate for 51 Peg's corona of T < ∼ 1 MK; the detected ACIS-S photons can be plausibly explained by emission lines of a very cool plasma near 200 eV. The constantly low X-ray surface flux and the flat-activity profile seen in optical Ca ii data suggest that 51 Peg is a Maunder minimum star; an activity enhancement due to a Hot Jupiter, as proposed by recent studies, seems to be absent. The star's X-ray fluxes in different instruments are consistent with the exception of the HRC Imager, which might have a larger effective area below 200 eV than given in the calibration.

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Determination of confidence limits for experiments with low numbers of counts

Cited by 477 publications

References 0 publications

The X-ray emission from Z Canis Majoris during an FUor-like outburst and the detection of its X-ray jet

The X-ray emission from Z Canis Majoris during an FUor-like outburst and the detection of its X-ray jet

Transition Region Emission from Very Low Mass Stars

51 Pegasi – a planet-bearing Maunder minimum candidate

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