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J/ApJ/660/1428      Astrometry around RX J0720.4-3125        (Kaplan+, 2007)

The distance to the isolated neutron star RX J0720.4-3125. Kaplan D.L., Van Kerkwijk M.H., Anderson J. <Astrophys. J., 660, 1428-1443 (2007)> =2007ApJ...660.1428K
ADC_Keywords: X-ray sources ; Positional data Keywords: astrometry - stars: individual (RX J0720.4-3125) - stars: neutron - X-rays: individual (RX J0720.4-3125) Abstract: We have used a set of dedicated astrometric data from the Hubble Space Telescope to measure the parallax and proper motion of the nearby neutron star RX J0720.4-3125. At each of eight epochs over 2 years, we used the High Resolution Camera of the Advanced Camera for Surveys to measure the position of the B=26.6 target to a precision of ∼2mas (∼0.07pix) relative to 22 other stars. From these data we measure a parallax of plx=2.8±0.9mas (for a distance of 360+170-90pc) and a proper motion of mu=107.8±1.2mas/yr. Exhaustive testing of every stage of our analysis suggests that it is robust, with a maximum systematic uncertainty on the parallax of 0.4mas. The distance is compatible with earlier estimates made from scaling the optical emission of RX J0720.4-3125 relative to the even closer neutron star RX J1856.5-3754. The distance and proper motion imply a transverse velocity of 180+90-40km/s, comparable to velocities observed for radio pulsars. The speed and direction suggest an origin for RX J0720.4-3125 in the Trumpler 10 OB association ∼0.7Myr ago, with a possible range of 0.5-1.0Myr given by the uncertainty in the distance. Description: Our main data set consists of 64 exposures taken during eight visits of the field of RX J0720.4-3125 with HST, between 04 Jul 2002 and 19 Mar 2004. All data were taken with the High Resolution Camera (HRC; with a plate scale of 28.27mas/pix) and the F475W (SDSS g') filter, which has good sensitivity to the blue colors of RX J0720.4-3125. Objects: ------------------------------------------------- RA (2000) DE Designation(s) ------------------------------------------------- 07 20 24.961 -31 25 50.21 X = RX J0720.4-3125 ------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table4.dat 70 23 *Astrometry of reference sources table7.dat 130 1172 ePSF position measurements for all exposures table9.dat 56 156 Merged positions for each epoch
Note on table4.dat: Object No. 117 not in table4.
Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
1- 3 A3 --- ID Object identifier (G1) 5 I1 --- o_ID [1/8] Number of epochs for which a source could be measured 7- 11 F5.1 mag mag Instrumental magnitude (2) 13- 21 F9.5 arcsec DRA Offset in right ascension (3) 23- 24 I2 10mas e_DRA rms uncertainty on DRA 27- 35 F9.5 arcsec DDE Offset in declination (3) 37- 39 I3 10mas e_DDE rms uncertainty on DDE 42- 47 F6.2 mas/yr pmRA Proper motion along RA (4) 49- 52 F4.2 mas/yr e_pmRA rms uncertainty on pmRA 55- 59 F5.2 mas/yr pmDE Proper motion along DE (4) 61- 64 F4.2 mas/yr e_pmDE rms uncertainty on pmDE 67- 70 F4.2 --- Rchi2 Reduced χ2 (5)
Note (2): Instrumental magnitudes defined as -2.5log10a, where a is the average amplitude of the effective PSF (ePSF) required to fit a given star in a single exposure. Note (3): Position offsets at MJD 52645.1, relative to star A, excluding parallactic offsets. Reference position: 07:20:24.4837-31:25:51.786 (J2000.0) Note (4): Proper motion relative to that of star A. The systematic uncertainty on the proper motion, from assuming that star A has mu=0, is ∼1mas/yr. Note (5): Reduced χ2 values for fitting, with degrees of freedom 2Nepoch-Npar, where the number of parameters Npar=5 for RX J0720.4-3125, 0 for A, and 4 for all other stars (note that these χ2red values for individual sources are not robust estimates.
Byte-by-byte Description of file: table7.dat
Bytes Format Units Label Explanations
1- 3 A3 --- ID Object identifier (G1) 5- 9 A5 --- Exp Exposure identifier (hrcNN) 11- 20 F10.5 pix DXpix Distortion-corrected X position 22- 28 F7.5 pix e_DXpix Uncertainty in Xpix 30- 39 F10.5 pix DYpix Distortion-corrected Y position 41- 47 F7.5 pix e_DYpix Uncertainty in Ypix 49- 53 F5.3 --- Num Number of bad pixel and distance to nearest bad one (1) 55- 62 F8.3 --- Rchi2 Reduced χ2 of the ePSF fit 64- 73 F10.5 pix Xpix Measured X position on chip 75- 81 F7.5 pix e_Xpix Uncertainty in Xpix 83- 92 F10.5 pix Ypix Measured Y position on chip 94-100 F7.5 pix e_Ypix Uncertainty in Ypix 102-110 F9.2 --- Amp Amplitude of effective PSF (ePSF) 112-117 F6.2 --- e_Amp Uncertainty in Amp 119-124 F6.3 --- Sky Sky level 126-130 F5.3 --- e_Sky Uncertainty in Sky (0 = fixed sky value)
Note (1): This is the sum of the number of bad pixels and the distance from the initial guess of the centroid to the nearest bad pixel, divided by 1000. Only measurements with values of 0 (no bad pixels) were used in our analysis.
Byte-by-byte Description of file: table9.dat
Bytes Format Units Label Explanations
1- 3 A3 --- ID Object identifier (G1) 5- 8 A4 --- Exp Exposure identifier (hrcN) 10- 19 F10.5 pix DXpix Distortion-corrected X position 21- 27 F7.5 pix e_DXpix Uncertainty in D-Xpix 29- 38 F10.5 pix DYpix Distortion-corrected Y position 40- 46 F7.5 pix e_DYpix Uncertainty in D-Ypix 48- 49 I2 --- Num Number of measurements (2x number of exposures) 51- 56 F6.3 --- Rchi2 Reduced χ2 (=χ2/(Num-6))
Global notes: Note (G1): Star number, with letters following Haberl et al. (1997A&A...326..662H), i.e. A = [HMB97] A = [KVA2007] 102 B = [HMB97] B = [KVA2007] 103 X = RX J0720.4-3125 = [KVA2007] 101 For other sources, [KVA2007] NNN in Simbad.
History: From electronic version of the journal
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 13-Mar-2009
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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