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Distances of Isolated neutron stars

with an introduction to neutron stars

Thomas Eisenbeiss

with

Fred Walter, Ralph Neuhäuser, Markus Hohle, Nina Tetzlaff,

and

Valeri Hambaryan

AIP Potsdam

Sep. 7th 2010

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 1 / 32


OUTLINE

1 MOTIVATION

2 THE MAGNIFICENT SEVEN

3 OTHER WAYS TO MEASURE DISTANCES

4 PARALLAX OF RX J1856.5-3754

5 THE DISTANCE TO RX J0720.4-3125

6 APPLICATIONS: THE BIRTHPLACE OF NEUTRON STARS

7 SUMMARY

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 2 / 32


MOTIVATION

Transition from observables (proper motion, flux, angular

diameter) to physical quantities (velocity, luminosity, physical

radius) depends the distance to some power

still no NS where we know mass and radius

M7 are great laboratories to study the surface of NS (Radius via

BB temp.)

important for velocity (radial velocity through bow shock)

age (origin, parent association)

confusion in the literature, very different values published.

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 3 / 32


1 MOTIVATION

2 THE MAGNIFICENT SEVEN

3 OTHER WAYS TO MEASURE DISTANCES

4 PARALLAX OF RX J1856.5-3754

5 THE DISTANCE TO RX J0720.4-3125

6 APPLICATIONS: THE BIRTHPLACE OF NEUTRON STARS

7 SUMMARY

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 4 / 32


THE DISCOVERY OF RX J1856.5-3754 NEAR CRA

WALTER ET AL. (1996)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 5 / 32


THE DISCOVERY OF RX J1856.5-3754 NEAR CRA

WALTER ET AL. (1996)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 5 / 32


THE DISCOVERY OF RX J1856.5-3754 NEAR CRA

WALTER ET AL. (1996)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 5 / 32


THE MAGNIFICENT SEVEN

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 6 / 32


THE MAGNIFICENT SEVEN

7 similar, initially unidentified, sources found in ROSAT survey

soft thermal X-ray emission

nearby (100−300 pc)

no radio emission detected so far

pulsations in X-rays (5)

gaussian absorption lines in X-ray spectra (3)

optical excess

may originate from the Gould Belt

Object kT Period Amplitude Optical PM Distance

eV s % mag mas/year pc

RX J0420.0−5022 44 3.45 13 B = 26.6 345

RX J0720.4−3125 87 8.39 11 B = 26.6 97 360

RX J0806.4−4123 96 11.37 6 B > 24 250

RBS 1223 86 10.31 18 m50ccd = 28.6 200 . . .

RX J1605.3+3249 96 − − B = 27.2 145 390

RX J1856.5−3754 60 7.06 1 V = 25.7 332 120

RBS 1774 101 9.44 4 R > 26 430

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 7 / 32


THE MAGNIFICENT SEVEN

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 7 / 32


THE MAGNIFICENT SEVEN

7 similar, initially unidentified, sources found in ROSAT survey

soft thermal X-ray emission

nearby (100−300 pc)

no radio emission detected so far

pulsations in X-rays (5)

gaussian absorption lines in X-ray spectra (3)

optical excess

may originate from the Gould Belt

Object kT Period Amplitude Optical PM Distance

eV s % mag mas/year pc

RX J0420.0−5022 44 3.45 13 B = 26.6 345

RX J0720.4−3125 87 8.39 11 B = 26.6 97 360

RX J0806.4−4123 96 11.37 6 B > 24 250

RBS 1223 86 10.31 18 m50ccd = 28.6 200 . . .

RX J1605.3+3249 96 − − B = 27.2 145 390

RX J1856.5−3754 60 7.06 1 V = 25.7 332 120

RBS 1774 101 9.44 4 R > 26 430

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 7 / 32


THE MAGNIFICENT SEVEN

Credit: R. Neuhäuser

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 7 / 32


THE MAGNIFICENT SEVEN

Credit: R. Neuhäuser

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 7 / 32


THE MAGNIFICENT SEVEN

Credit: R. Neuhäuser

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 7 / 32


1 MOTIVATION

2 THE MAGNIFICENT SEVEN

3 OTHER WAYS TO MEASURE DISTANCES

4 PARALLAX OF RX J1856.5-3754

5 THE DISTANCE TO RX J0720.4-3125

6 APPLICATIONS: THE BIRTHPLACE OF NEUTRON STARS

7 SUMMARY

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 8 / 32


LESSONS TO LEARN FROM HYDROGEN

X-ray radiation of M7 absorbed by interstellar hydrogen

M7 are soft X-ray sources −→ nearby

proper model of hydrogen distribution in the galaxy gives a

measure to the distance of neutron stars (Posselt et al. 2007)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 9 / 32


LESSONS TO LEARN FROM HYDROGEN

NH PREDICTED BY ANALYTICAL MODEL

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 9 / 32


LESSONS TO LEARN FROM HYDROGEN

NH DISTRIBUTION WITH DISTANCE AND GALACTIC LONGITUDE

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 9 / 32


LESSONS TO LEARN FROM HYDROGEN

Distances obtained for the M7

The NH was obtained by blackbody and absorption line XSPEC-fits

from XMM-Newton EPIC-pn observations (Posselt et al. 2007).

name N(H) (#lines) dana dext dana130

[10 20 cm −2 ] [pc] [pc] [pc]

RX J1856.5-3754 0.7 (0L) 135 135 125

RX J0420.0-5022 1.6 (1L) 345 · · · 325

RX J0720.4-3125 1.2 (1L) 270 235 265

RX J0806.4-4123 1.0 (1L) 250 235 240

RBS 1223 4.3 (1L) · · · · · · · · ·

RX J1605.3+3249 2.0 (3L) 390 · · · 325

RBS 1774 2.4 (1L) 430 · · · 390

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 9 / 32


1 MOTIVATION

2 THE MAGNIFICENT SEVEN

3 OTHER WAYS TO MEASURE DISTANCES

4 PARALLAX OF RX J1856.5-3754

5 THE DISTANCE TO RX J0720.4-3125

6 APPLICATIONS: THE BIRTHPLACE OF NEUTRON STARS

7 SUMMARY

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 10 / 32


THE MOST NEARBY INS RX J1856.5-3754

discovered by Walter et al. (1996)

optical counterpart identified by Walter & Matthews (1997), blue,

V∼ 25.7

X-ray spectrum is pure blackbody with kT = 63 eV (Burwitz et al.

2003)

no evidence for absorption

bow shock nebula found in Hα emission (van Kerwijk & Kulkarni

2001)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 11 / 32


THE MOST NEARBY INS RX J1856.5-3754

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 11 / 32


THE MOST NEARBY INS RX J1856.5-3754

discovered by Walter et al. (1996)

optical counterpart identified by Walter & Matthews (1997), blue,

V∼ 25.7

X-ray spectrum is pure blackbody with kT = 63 eV (Burwitz et al.

2003)

no evidence for absorption

bow shock nebula found in Hα emission (van Kerwijk & Kulkarni

2001)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 11 / 32


THE MOST NEARBY INS RX J1856.5-3754

Burwitz et al. (2003)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 11 / 32


THE MOST NEARBY INS RX J1856.5-3754

discovered by Walter et al. (1996)

optical counterpart identified by Walter & Matthews (1997), blue,

V∼ 25.7

X-ray spectrum is pure blackbody with kT = 63 eV (Burwitz et al.

2003)

no evidence for absorption

bow shock nebula found in Hα emission (van Kerwijk & Kulkarni

2001)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 11 / 32


THE MOST NEARBY INS RX J1856.5-3754

van Kerkwijk & Kulkarni (2001)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 11 / 32


EARLIER MEASUREMENTS OF THE DISTANCE

1 close to Corona Australis (120-140 pc)

2 interstellar extinction models (Posselt et al. 2007) 125-135 pc

3 Walter (2001) 61 pc based on 3 HST/WFPC2 images → ERROR

4 Kaplan et al. (2002) published 140 pc

5 incorporating a fourth WFPC2 image Walter & Lattimer (2002)

found 117 ± 12 pc

6 Kaplan et al. (2007) reported 167 +18

−15 pc

7 van Kerkwijk & Kaplan (2007) measured 161 +18

−14 pc

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 12 / 32


EARLIER MEASUREMENTS OF THE DISTANCE

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 12 / 32


EARLIER MEASUREMENTS OF THE DISTANCE

1 close to Corona Australis (120-140 pc)

2 interstellar extinction models (Posselt et al. 2007) 125-135 pc

3 Walter (2001) 61 pc based on 3 HST/WFPC2 images → ERROR

4 Kaplan et al. (2002) published 140 pc

5 incorporating a fourth WFPC2 image Walter & Lattimer (2002)

found 117 ± 12 pc

6 Kaplan et al. (2007) reported 167 +18

−15 pc

7 van Kerkwijk & Kaplan (2007) measured 161 +18

−14 pc

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 12 / 32


THE CHALLENGE

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 13 / 32


THE CHALLENGE

astrometric observations require:

1 large plate scale

2 large field of view

RX J1856 observed on 8 occasion over 2 years with HST

ACS/HRC

PLATE SCALE

28.27 mas small motions

measurable

FIELD OF VIEW

30 arcsec, limited number of

ref. stars

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 14 / 32


THE PROBLEM OF PIXEL-PHASE ERRORS

Anderson & King (2001)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 15 / 32


THE PROBLEM OF PIXEL-PHASE ERRORS

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 15 / 32


THE PROBLEM OF PIXEL-PHASE ERRORS

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 15 / 32


THE PROBLEM OF PIXEL-PHASE ERRORS

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 15 / 32


THE SOLUTION: THE EFFECTIVE PSF

new empirical definition of PSF:

ΨE(∆x, ∆y) = Pij − s∗

f∗: flux of star, s∗: noise, Pij: pixel(i, j),

ΨE(∆x, ∆y): ePSF of star at (x, y)

lots of observations of GC 47-Tuc at

lots of pointings, filters, orientations

iterative, self-calibrating approach to

determine empirical ePSF

f∗

Anderson & King (2004)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 16 / 32


THE SOLUTION: THE EFFECTIVE PSF

new empirical definition of PSF:

ΨE(∆x, ∆y) = Pij − s∗

f∗: flux of star, s∗: noise, Pij: pixel(i, j),

ΨE(∆x, ∆y): ePSF of star at (x, y)

lots of observations of GC 47-Tuc at

lots of pointings, filters, orientations

iterative, self-calibrating approach to

determine empirical ePSF

f∗

Anderson & King (2004)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 16 / 32


THE SOLUTION: THE EFFECTIVE PSF

new empirical definition of PSF:

ΨE(∆x, ∆y) = Pij − s∗

f∗: flux of star, s∗: noise, Pij: pixel(i, j),

ΨE(∆x, ∆y): ePSF of star at (x, y)

lots of observations of GC 47-Tuc at

lots of pointings, filters, orientations

f∗

iterative, self-calibrating approach to

determine empirical ePSF Anderson & King (2004)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 16 / 32


FIELD DISTORTIONS (ANDERSON & KING 2004)

DISTORTION TYPES

skew (deviation from perpendicularity, ≈ 9 ◦ )

non-linear distortions

TWO STEPS

1 the polynomial solution

iterative self-calibration

2 the fine scale solution

linearly interpolated look-up table 65 × 65 points

Everything is transformed to a common reference frame with pixel

scale of 0.02827 arcsec/pix.

Final accuracy achieved 0.01 pix

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 17 / 32


FIELD DISTORTIONS (ANDERSON & KING 2004)

DISTORTION TYPES

skew (deviation from perpendicularity, ≈ 9 ◦ )

non-linear distortions

TWO STEPS

1 the polynomial solution

iterative self-calibration

2 the fine scale solution

linearly interpolated look-up table 65 × 65 points

Everything is transformed to a common reference frame with pixel

scale of 0.02827 arcsec/pix.

Final accuracy achieved 0.01 pix

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 17 / 32


FIELD DISTORTIONS (ANDERSON & KING 2004)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 17 / 32


FIELD DISTORTIONS (ANDERSON & KING 2004)

DISTORTION TYPES

skew (deviation from perpendicularity, ≈ 9 ◦ )

non-linear distortions

TWO STEPS

1 the polynomial solution

iterative self-calibration

2 the fine scale solution

linearly interpolated look-up table 65 × 65 points

Everything is transformed to a common reference frame with pixel

scale of 0.02827 arcsec/pix.

Final accuracy achieved 0.01 pix

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 17 / 32


FIELD DISTORTIONS (ANDERSON & KING 2004)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 17 / 32


FIELD DISTORTIONS (ANDERSON & KING 2004)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 17 / 32


FIELD DISTORTIONS (ANDERSON & KING 2004)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 17 / 32


FIELD DISTORTIONS (ANDERSON & KING 2004)

DISTORTION TYPES

skew (deviation from perpendicularity, ≈ 9 ◦ )

non-linear distortions

TWO STEPS

1 the polynomial solution

iterative self-calibration

2 the fine scale solution

linearly interpolated look-up table 65 × 65 points

Everything is transformed to a common reference frame with pixel

scale of 0.02827 arcsec/pix.

Final accuracy achieved 0.01 pix

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 17 / 32


FIELD DISTORTIONS (ANDERSON & KING 2004)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 17 / 32


FIELD DISTORTIONS (ANDERSON & KING 2004)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 17 / 32


FIELD DISTORTIONS (ANDERSON & KING 2004)

DISTORTION TYPES

skew (deviation from perpendicularity, ≈ 9 ◦ )

non-linear distortions

TWO STEPS

1 the polynomial solution

iterative self-calibration

2 the fine scale solution

linearly interpolated look-up table 65 × 65 points

Everything is transformed to a common reference frame with pixel

scale of 0.02827 arcsec/pix.

Final accuracy achieved 0.01 pix

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 17 / 32


THE MODEL

We fit the positions of each star in each image using


Xcor

Ycor



� �

cos θ − sin θ x

= (1 − η)

sin θ cos θ y

� � � � �

∆x

µx

+ + ∆t + Π

∆y

µy

η: scale correction, θ: rel. orientation, ∆x/y: rel. offset, µ:

proper motion, Π: parallaxe, p: parallactic displacement in each

frame

fitted by various χ 2 minimization algorithms (Walter, Eisenbeiss et al.

2010, submitted to ApJ)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 18 / 32

px

py



MY OWN APPROACH IN DETAIL

PREPARATIONS

Measure Positions of stars

using Anderson’s PSF and

distortion solution (Anderson &

King 2004)

Measure uncertainties with

IDL XStarFinder

shift and rotate each image to

the common reference frame

and assign stars in each

image

measure inter-object distances

in each image to identify

disturbed detections

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 19 / 32


MY OWN APPROACH IN DETAIL

PREPARATIONS

Measure Positions of stars

using Anderson’s PSF and

distortion solution (Anderson &

King 2004)

Measure uncertainties with

IDL XStarFinder

shift and rotate each image to

the common reference frame

and assign stars in each

image

measure inter-object distances

in each image to identify

disturbed detections

corrected instrumental magnitude

−15

−14

−13

−12

−11

−10

−9

−8

−7

−6

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

square root of sum of squares of x and y uncertainties

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 19 / 32


MY OWN APPROACH IN DETAIL

PREPARATIONS

Measure Positions of stars

using Anderson’s PSF and

distortion solution (Anderson &

King 2004)

Measure uncertainties with

IDL XStarFinder

shift and rotate each image to

the common reference frame

and assign stars in each

image

measure inter-object distances

in each image to identify

disturbed detections

y pixel

1000

900

800

700

600

570

500 568

400 566

300 564

200

100

8 6

7

5

1

2

3

4

562

480 490 500 510

NS

0 200 400 600

x pixel

800 1000

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 19 / 32


MY OWN APPROACH IN DETAIL

PREPARATIONS

Measure Positions of stars

using Anderson’s PSF and

distortion solution (Anderson &

King 2004)

Measure uncertainties with

IDL XStarFinder

shift and rotate each image to

the common reference frame

and assign stars in each

image

measure inter-object distances

in each image to identify

disturbed detections

y pixel

1000

900

800

700

600

500

400

300

200

100

0 200 400 600

x pixel

800 1000

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 19 / 32


MY OWN APPROACH IN DETAIL

FITTING PROCEDURE












initially µ and Π are zero

Frame related quantities (θ, η, ∆x, ∆y) are varied by small amount

χ 2 for all combinations of those is calculated (including the

unchanged vaules), best χ 2 is chosen

Star related (µx, µy) is calculated by a least square fit

Π is incorporated as variations (px, py) to the p.m. fit. A parallax Π

is accepted if the rms of the p.m fit is reduced

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 20 / 32




RESULTS

THE PATH OF RX J1856

y pixel

567.5

567

566.5

566

565.5

565

564.5

564

563.5

480 485 490 495 500 505

x pixel

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 21 / 32


RESULTS

RELATIVE PARALLACTIC DISPLACEMENT OVER TIME

x pixel

503.6

503.5

503.4

503.3

503.2

503.1

503

502.9

502.8

5.25 5.26 5.27 5.28 5.29 5.3 5.31 5.32

x 10 4

502.7

Modified Julian Date

y pixel

567.6

567.55

567.5

567.45

567.4

567.35

567.3

567.25

567.2

567.15

5.25 5.26 5.27 5.28 5.29 5.3 5.31 5.32

x 10 4

567.1

Modified Julian Date

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 21 / 32


RESULTS

PARALLACTIC ELLIPSE

y pixel

567.6

567.55

567.5

567.45

567.4

567.35

567.3

567.25

567.2

567.15

567.1

502.7 502.8 502.9 503 503.1 503.2 503.3 503.4 503.5 503.6

x pixel

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 21 / 32


RESULTS

SUMMARY

Star XP IX YP IX PLX [mas] DIST [pc] µα [mas] µδ [mas] µ [mas]

1 149.924 ± 0.022 745.427 ± 0.026 −0.26 ± 0.96 −3800 +Inf

−−5300 11.52 ± 0.56 1.51 ± 0.89 11.62 ± 0.67

2 155.687 ± 0.018 747.662 ± 0.013 0.37 ± 0.63 2700 +Inf

−1700 3.39 ± 0.3 −4.04 ± 0.29 5.274 ± −0.029

3 212.438 ± 0.031 1012.54 ± 0.03 −0.2 ± 1.2 −5000 +Inf

−−5200 6.48 ± 0.66 −0.63 ± 0.54 6.51 ± 0.6

4 316.827 ± 0.038 683.772 ± 0.029 0.5 ± 1.4 2000 +Inf

−1600 2.64 ± 0.61 5.24 ± 0.7 5.87 ± 0.9

5 395.435 ± 0.017 780.559 ± 0.039 −0.6 ± 1.2 −1700 +Inf

−−3300 5.07 ± 0.49 3.38 ± 0.71 6.09 ± 0.8

6 385.202 ± 0.0089 699.099 ± 0.012 1.29 ± 0.42 780 +380

−190 −9.78 ± 0.18 6.83 ± 0.23 11.929 ± −0.016

7 319.969 ± 0.021 172.882 ± 0.02 0.42 ± 0.82 2400 +Inf

−1600 4.36 ± 0.43 −3.52 ± 0.43 5.604 ± 0.064

8 475.05 ± 0.0035 972.636 ± 0.003 −0.18 ± 0.13 −6000 +Inf

−13000 0.363 ± 0.091 −1.607 ± 0.073 1.647 ± −0.051

9 552.593 ± 0.011 986.234 ± 0.0056 −0.41 ± 0.35 −2000 +Inf

−16000 6.26 ± 0.44 0.57 ± 0.19 6.29 ± 0.46

10 503.217 ± 0.028 567.298 ± 0.019 8.15 ± 0.96 123 +16

−13 −324.26 ± 0.79 −59.22 ± 0.75 329.62 ± −0.91

11 654.762 ± 0.0062 839.625 ± 0.009 −0.26 ± 0.31 −4000 +Inf

−−25000 4.72 ± 0.11 −0.52 ± 0.21 4.749 ± 0.086

12 598.045 ± 0.007 97.9245 ± 0.0042 0.38 ± 0.23 2630 +3900

−970 6.6 ± 0.1 0.526 ± 0.077 6.62 ± 0.11

13 704.574 ± 0.016 601.568 ± 0.035 −0.2 ± 1.1 −5000 +Inf

−−5300 9.16 ± 0.49 −5.86 ± 0.58 10.87 ± 0.1

14 835.407 ± 0.01 831.928 ± 0.035 −0.4 ± 1 −2500 +Inf

−−4300 3.79 ± 0.15 −3.17 ± 0.53 4.94 ± −0.22

15 730.841 ± 0.0073 170.76 ± 0.0047 0.6 ± 0.25 1670 +1200

−490 −2.469 ± 0.063 1.356 ± 0.077 2.817 ± −0.018

16 710.679 ± 0.0052 37.1137 ± 0.0083 0.02 ± 0.28 50000 +Inf

−53000 4.76 ± 0.13 −1.59 ± 0.27 5.019 ± 0.038

17 866.685 ± 0.018 565.188 ± 0.035 0.8 ± 1.1 1250 +Inf

−690 0.73 ± 0.34 −1.4 ± 0.41 1.58 ± −0.21

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 21 / 32


RESULTS

PROBABILITY DISTRIBUTION OF THE DIFFERENT MODELS

Walter et al. 2010 submitted

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 21 / 32


RESULTS

ALL MODELS

Parallax: Π = (8.18 ± 0.24) mas

Proper motion: µ = (332.0 ± 1.9) mas/yr

PA = (100.3 ± 0.3) ◦

Distance: d = 122 +11

−15 pc

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 21 / 32


1 MOTIVATION

2 THE MAGNIFICENT SEVEN

3 OTHER WAYS TO MEASURE DISTANCES

4 PARALLAX OF RX J1856.5-3754

5 THE DISTANCE TO RX J0720.4-3125

6 APPLICATIONS: THE BIRTHPLACE OF NEUTRON STARS

7 SUMMARY

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 22 / 32


THINGS TO KNOW ABOUT RX J0720.4-3125

identified as INS in 1997 (Haberl et al.)

optical counterpart by Kulkarni & van Kerkwijk 1998

proper motion 97 ± 12 mas/yr measured by Motch et al. (2003)

with FORS 1

optical excess SED looks more like PL rather than BB (Kaplan et

al. 2003, Motch et al. 2003), origin of optical flux might be NS

surrounding (Hambaryan et al. 2009), not NS surface

Long term variations in X-Ray SED discovered (de Vries et al.

2004) and interpreted as precession (Haberl et al. 2004, Hohle et

al. 2010) or Glitch (van Kerkwijk e tal. 2007)

Distance 360 +170

−90 and proper motion 107.8 ± 1.2 with HST/ACS

by Kaplan et al. (2007)

V magnitude 26.81 ± 0.09 (Eisenbeiss et al. 2010) with FORS

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 23 / 32


THINGS TO KNOW ABOUT RX J0720.4-3125

Motch et al. (2003)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 23 / 32


THINGS TO KNOW ABOUT RX J0720.4-3125

identified as INS in 1997 (Haberl et al.)

optical counterpart by Kulkarni & van Kerkwijk 1998

proper motion 97 ± 12 mas/yr measured by Motch et al. (2003)

with FORS 1

optical excess SED looks more like PL rather than BB (Kaplan et

al. 2003, Motch et al. 2003), origin of optical flux might be NS

surrounding (Hambaryan et al. 2009), not NS surface

Long term variations in X-Ray SED discovered (de Vries et al.

2004) and interpreted as precession (Haberl et al. 2004, Hohle et

al. 2010) or Glitch (van Kerkwijk e tal. 2007)

Distance 360 +170

−90 and proper motion 107.8 ± 1.2 with HST/ACS

by Kaplan et al. (2007)

V magnitude 26.81 ± 0.09 (Eisenbeiss et al. 2010) with FORS

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 23 / 32


THINGS TO KNOW ABOUT RX J0720.4-3125

�F � [Hz erg/s/cm 2 /Hz]

10 �10

10 �11

10 �12

10 �13

10 �14

10 �15

10 14

10 �16

H

up

R

V

B

U

10 15

10 16

frequency [Hz]

10 17

Eisenbeiss et al. (2010)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 23 / 32

10 18


THINGS TO KNOW ABOUT RX J0720.4-3125

identified as INS in 1997 (Haberl et al.)

optical counterpart by Kulkarni & van Kerkwijk 1998

proper motion 97 ± 12 mas/yr measured by Motch et al. (2003)

with FORS 1

optical excess SED looks more like PL rather than BB (Kaplan et

al. 2003, Motch et al. 2003), origin of optical flux might be NS

surrounding (Hambaryan et al. 2009), not NS surface

Long term variations in X-Ray SED discovered (de Vries et al.

2004) and interpreted as precession (Haberl et al. 2004, Hohle et

al. 2010) or Glitch (van Kerkwijk e tal. 2007)

Distance 360 +170

−90 and proper motion 107.8 ± 1.2 with HST/ACS

by Kaplan et al. (2007)

V magnitude 26.81 ± 0.09 (Eisenbeiss et al. 2010) with FORS

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 23 / 32


THINGS TO KNOW ABOUT RX J0720.4-3125

Kalpan et al. (2007)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 23 / 32


THINGS TO KNOW ABOUT RX J0720.4-3125

MJD−50,000 (days)

∆ δ (mas)

5

0

−5

3000

2900

2800

2700

2600

2500

2400

5

5

∆ α (mas)

0

0

∆ α (mas)

−5

−5

2500 2700 2900 3100

5

50

Kalpan et al. (2007)

MJD−50,000 (days)

0 −50 −100

∆ α (mas)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 23 / 32

0

−5

100

50

0

−50

∆ δ (mas)

∆ δ (mas)


THINGS TO KNOW ABOUT RX J0720.4-3125

identified as INS in 1997 (Haberl et al.)

optical counterpart by Kulkarni & van Kerkwijk 1998

proper motion 97 ± 12 mas/yr measured by Motch et al. (2003)

with FORS 1

optical excess SED looks more like PL rather than BB (Kaplan et

al. 2003, Motch et al. 2003), origin of optical flux might be NS

surrounding (Hambaryan et al. 2009), not NS surface

Long term variations in X-Ray SED discovered (de Vries et al.

2004) and interpreted as precession (Haberl et al. 2004, Hohle et

al. 2010) or Glitch (van Kerkwijk e tal. 2007)

Distance 360 +170

−90 and proper motion 107.8 ± 1.2 with HST/ACS

by Kaplan et al. (2007)

V magnitude 26.81 ± 0.09 (Eisenbeiss et al. 2010) with FORS

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 23 / 32


RESULTS OF PARALLAX REDETERMINATION

THE PATH OF RX J0720

y pixel

554.5

554

553.5

553

552.5

552

551.5

551

550.5

335 336 337 338 339 340 341 342

x pixel

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 24 / 32


RESULTS OF PARALLAX REDETERMINATION

RELATIVE PARALLACTIC DISPLACEMENT OVER TIME

x pixel

336.2

336.15

336.1

336.05

336

335.95

335.9

335.85

335.8

335.75

5.24 5.25 5.26 5.27 5.28 5.29 5.3 5.31

x 10 4

Modified Julian Date

y pixel

550.9

550.8

550.7

550.6

550.5

550.4

550.3

550.2

5.24 5.25 5.26 5.27 5.28 5.29 5.3 5.31

x 10 4

550.1

Modified Julian Date

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 24 / 32


RESULTS OF PARALLAX REDETERMINATION

PARALLACTIC ELLIPSE

y pixel

550.9

550.8

550.7

550.6

550.5

550.4

550.3

550.2

550.1

335.75 335.8 335.85 335.9 335.95

x pixel

336 336.05 336.1 336.15 336.2

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 24 / 32


RESULTS OF PARALLAX REDETERMINATION

SUMMARY

Star XP IX YP IX PLX [mas] DIST [pc] µα [mas] µδ [mas] µ [mas]

1 784.022 ± 0.018 177.461 ± 0.011 −0.2 ± 0.6 −5000 +Inf

−−7500 −0.33 ± 0.15 −0.99 ± 0.11 1.04 ± −0.15

2 218.884 ± 0.0083 208.206 ± 0.016 −0.15 ± 0.51 −6700 +Inf

−−9300 0.496 ± 0.089 −0.05 ± 0.13 0.499 ± 0.076

3 131.906 ± 0.023 231.958 ± 0.027 −0.5 ± 1 −2000 +Inf

−−4000 0.72 ± 0.83 −0.23 ± 0.61 0.76 ± 0.61

4 61.503 ± 0.0095 398.249 ± 0.016 −0 ± 0.53 −Inf +Inf

−−330000 −0.39 ± 0.33 1.31 ± 0.23 1.37 ± 0.13

5 797.317 ± 0.0039 417.845 ± 0.014 0.1 ± 0.41 10000 +Inf

−8400 0.13 ± 0.11 0.73 ± 0.13 0.74 ± 0.15

6 929.429 ± 0.011 451.721 ± 0.014 0.55 ± 0.5 1820 +20000

−870 1.13 ± 0.2 0.1 ± 0.22 1.13 ± 0.22

7 553.945 ± 0.0073 491.21 ± 0.0077 −0.23 ± 0.3 −4000 +Inf

−−18000 −0.08 ± 0.1 −0.32 ± 0.16 0.33 ± −0.18

8 760.61 ± 0.012 498.942 ± 0.016 0.61 ± 0.57 1640 +21000

−780 −0.16 ± 0.22 1.73 ± 0.25 1.74 ± 0.23

9 335.972 ± 0.023 550.582 ± 0.053 3.6 ± 1.6 278 +210

−84 92.8 ± 1.4 55.3 ± 1.7 108 ± 2.1

10 405.477 ± 0.028 634.478 ± 0.041 0.1 ± 1.4 10000 +Inf

−6300 1.1 ± 1.6 −0.6 ± 0.85 1.25 ± 1

11 433.092 ± 0.03 687.157 ± 0.032 −0.8 ± 1.2 −1300 +Inf

−−3800 −2.6 ± 1 −3.33 ± 0.67 4.2 ± −1.1

12 951.121 ± 0.021 751.333 ± 0.0059 0.43 ± 0.62 2300 +Inf

−1400 −0.08 ± 0.45 −0.33 ± 0.25 0.34 ± −0.35

13 482.716 ± 0.037 857.162 ± 0.013 0.3 ± 1.1 3300 +Inf

−2700 −0.75 ± 0.34 −0.82 ± 0.2 1.11 ± −0.38

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 24 / 32


DIFFERENCES AND SIMILARITIES BETWEEN KAPLAN ET

AL. (2007) AND EISENBEISS ET AL (IN PREP)

SIMILARITIES

Data set

Data reduction and general approach

Anderson’s PSF

DIFFERENCES

Kaplan co-alligned inter Epoch images as good as possible, took

the weighted mean of positions and continued with fitting.

Kaplan et al. did not use Anderson’s distortion correction

Kaplan et al. fitted a skew term as additional parameter and

allowed for different scales in x and y

Differences in the selection criteria of ”good stars” (main issue)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 25 / 32


COMPARISON OF THE RESULTS

RX J1856

Posselt[07] Kaplan[07] Walter[subm]

Distance ≈ 135 ± 25 167 +18

−14

RX J0720

122 +11

−15

Posset[07] Kaplan[07] Eisenbeiss[inprep]

Distance ≈ 270 ± 25 360 +170

−90

278 +210

−84

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 26 / 32


1 MOTIVATION

2 THE MAGNIFICENT SEVEN

3 OTHER WAYS TO MEASURE DISTANCES

4 PARALLAX OF RX J1856.5-3754

5 THE DISTANCE TO RX J0720.4-3125

6 APPLICATIONS: THE BIRTHPLACE OF NEUTRON STARS

7 SUMMARY

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 27 / 32


THE BIRTHPLACE OF NEUTRON STARS

Age upper limit can be estimated by decrease of rotation period:

3.8 Myr (van Kerkwijk & Kaplan 2008) for RX J1856.4-3754

1.9 Myr (Kaplan 2008) for RX J0720.4-3125

Independent age estimation by tracing back the neutron star to the origin (Tetzlaff et al. 2010)

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 28 / 32


THE BIRTHPLACE OF NEUTRON STARS

Distribution of O-stars (gray) and Pulsars (red), M7 are blue stars. Young stellar associations are

marked with circle.

FIGURE: Tetzlaff et al. 2010

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 28 / 32


THE BIRTHPLACE OF NEUTRON STARS

Runaway O and B stars (black) and Neutron stars with known proper motion (blue stars). NS are

traced back (2 Myr) to there counterpart / originating association. Successful already in the case

of PSR B1929 which is the suggested counterpart of ζ Ophiuchi (Hoogerwerf 2001).

FIGURE: Tetzlaff et al. 2010

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 28 / 32


THE POTENTIAL BIRTHPLACES OF

RX J1856.5-3754

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 29 / 32


THE POTENTIAL BIRTHPLACES OF

RX J0720.4-3125

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 29 / 32


THE POTENTIAL BIRTHPLACES OF

radial velocity unknown

Limitations:

true distance for most neutron stars uncertain

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 29 / 32


1 MOTIVATION

2 THE MAGNIFICENT SEVEN

3 OTHER WAYS TO MEASURE DISTANCES

4 PARALLAX OF RX J1856.5-3754

5 THE DISTANCE TO RX J0720.4-3125

6 APPLICATIONS: THE BIRTHPLACE OF NEUTRON STARS

7 SUMMARY

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 30 / 32


SUMMARY

RX J1856.5-3754

Our distance is consistent with previously published values (Walter et

al. 2002, Kaplan et al. 2002, Posselt et al. 2007), but not consistent

recently mentioned values.

RX J0720.4-3125

Our distance is consistent with previously published values (Kaplan et

al. 2007, van Kerkwijk et al. 2007, Posselt et al. 2007), but no

improvement in accuracy could be achieved.

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 31 / 32


END OF THE TALK

Thank you for your attention

Thomas Eisenbeiss (AIP) Distance of XDINS Sep. 7th 10 32 / 32

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