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Notes for object MESSIER 081

48 note(s) found in NED.

1. 2012ApJ...754...67F
Re:NGC 3031
NGC 3031 .SAS2..-M81, interacting with the M81 group. Prominent central emission
features connected to a liner-type activity prevent us from deriving the central
kinematics (r < +/-2 arcsec) reliably. This galaxy exhibits an interesting shape
of its velocity dispersion profile. The profile first rises gradually until
~=150 km s^-1^ at radius of about 25". It then drops quickly to a minimum of
about 130 km s^-1^ at 18" and rises then again to ~=160 km s^-1^ at the center.
The drop around 18" is accompanied by a rapid change of slope of the rotational
velocity which stays relatively flat outward of this radius and a strengthening
of the h_3_ moments. Also the otherwise vanishing h_4_ moments rise to positive
values (~=0.1) at r ~= 15" where they form the most prominent double peak
feature of our sample. The minor axis profile shows similar local minima in the
dispersion profile that are accompanied by local maxima in the h_4_ moments at
radii of about 9". Given the inclination of 59^deg^ this points to a flattened
structure within the bulge.

2. 2011AJ....141...23B
Re:NGC 3031
A.9. NGC 3031
NGC 3031, also known as M 81, is a grand-design spiral
galaxy located at a distance of 3.6 Mpc. The analysis of
NGC 3031 revealed 321 HI holes, the largest number of holes
detected in any of the galaxies in this sample. This is due to
various factors such as its relatively large size, close proximity,
and high spatial resolution of the observations. We were able
to detect holes down to ~80 pc which led to the detection of a
wealth of small holes; almost 90% of the total holes detected
have a size less than 200 pc. Only a handful of supershells were
detected. The mean kinetic age is 7.8Myr with 80% of the holes
being younger than 9Myr. Several features detected (holes nos.:
34, 72, 88, 93, 94, 97, 99, 102, 106, 109, 113, 114, 170, 255,
and 273) are probably not genuine holes but the result of the
warp in the HI disk. Due to its large angular size, M 81 was
divided into six areas (panels (C9).(C15) in the online version
of Figure 30) to be able to show all detected holes.

3. 2009ApJ...703.1034Y
M 81. We cannot model the X-ray emission using an ADAF component alone. In
contrast to our result, Quataert et al. (1999) can fit the X-ray spectrum with
an ADAF. The reason for the discrepancy is that the mass of the black hole they
adopt is ~20 times smaller than ours. On the other hand, the X-ray spectrum is
well fitted by the jet (see also Markoff et al. 2008), although the value of p
in the jet model (1.8) is again formally smaller than 2.

4. 2009A&A...502..457G
Re:NGC 3031
A.1.3 NGC 3081 From a combined Swift and INTEGRAL analysis, Beckmann et al.
(2007) find {GAMMA} = 1.8+/-0.2 with L_20-100_ = 8.1 x 10^42^ erg s^-1^. They
also find significant variability of a factor of a few in the BAT 14-195 keV
lightcurve over a 15 month period.
Fitting an absorbed PL above a few keV (the softer flux is fit by weak
scattering or a blackbody) to spectra extracted from the Tartarus database gives
N_H_ = 68(+/-5) x 10^22^ cm^-2^ with L_2-10_ 4-6 x 10^42^ erg s^-1^, the
variation being the one between the ASCA SISs. Extending the de-absorbed PL to
200 keV gives L_14-195_ = 9-14 x 10^42^ erg s^-1^, matching the more recent
values quoted by Markwardt et al. (2005) and Ajello et al. (2008). This suggests
that variability may not be very strong.
On the other hand, BeppoSAX is known to have observed the source in a low
flux state (Maiolino et al. 1998). We take the lower value of the luminosity
range found in the above ASCA fits, with a large error of log L = 0.3 as a mean
This source was also imaged by Krabbe et al. (2001) at 1.3" resolution.
The full N-band flux quoted by them is consistent with our narrow-band PAH2 flux
(assuming a flat SED in {lambda}F_{lambda}_ units), implying the absence of
extended emission on ~1" scales.

5. 2008MNRAS.386.2242H
Re:NGC 3031
NGC 224 (M31), NGC 3031 (M81) and NGC 3115 in our sample are typical classical
bulges listed in KK04.

6. 2008AJ....136.2648D
Re:NGC 3031
4.7. NGC 3031 Better known as M81, this galaxy is the prototypical grand-design
spiral and together with M82 and NGC 3077 forms an interacting system, (e.g.,
van der Hulst 1997; Yun et al. 1994). A previous determination of the H I
rotation curve was by Visser (1978, 1980). We compare our results in Figure 11
after correction to the same distance scale. We find excellent agreement overall
between his and our rotation curves where they overlap in radius. The
differences we find are all attributable to different local values for P.A. and
i: we allow i and P.A. to change with radius, whereas Visser (1980) uses a
constant inclination of 59{degree} and a P.A. value of 329{degree}. However,
these constant values agree, well with our average values of 59^deg^ and
330.2^deg^, respectively.

7. 2008AJ....136.2648D
Re:NGC 3031
6.6. NGC 3031 The surface brightness profiles of NGC 3031 are shown in Figure
34. The 2MASS J, H, and K profiles can be traced out to ~750", and the 3.6 {mu}m
profile out to ~850". The profiles show clear evidence for a central component.
The outer disk shows a gradual flattening of the surface brightness profile
toward larger radii. We modeled the central component using an exponential disk
with parameters {mu}_0_ = 12.2 mag arcsec^-2^ and h = 0.25 kpc. To describe the
outer disk we simply subtracted the central exponential disk from the total
light profile. The slight (~0.2 mag) residuals seen around R ~ 100" do not
impact on any subsequent modeling. The (J - K) color profile shows no
significant color gradient, except for a central redder component. We assume a
constant {GAMMA}^3.6^_*_ = 0.8 for the disk and {GAMMA}^3.6^_*_ = 1.0 for the
central component. The rotation curve mass models are shown in Figure 35. At
first glance, it is already clear that the model fits deviate significantly from
the observed rotation curve. Although the general trends in the curve are
described well, smaller scale deviations clearly indicate the presence of
significant noncircular motions. Given the presence of the prominent,
grand-design spiral arms (causing the bump at R ~ 7.5 kpc), and M81's location
in an interacting system, this should not come as a surprise. The fit with fixed
{GAMMA}^3.6^_*_ yields {chi}^2^_r_ values that are only slightly inferior to the
free {GAMMA}^3.6^_*_ fits.

8. 2007MNRAS.382.1552L
Re:NGC 3031
NGC 3031 - M81: This is a well-known nearby Seyfert 1 nucleus (Peimbert &
Torres-Peimbert 1981b; Shuder & Osterbrock 1981). The nucleus is very bright,
and is unresolved in HST images, with an upper limit to its diameter of 0.73 pc
(Devereux & Ford 1997). There is a nuclear variable radio source with a core-jet
morphology (Bietenholz et al. 2000).

9. 2007MNRAS.377.1696M
M81 (NGC 3031). Bietenholz, Bartel & Rupen (2000) used VLBI to measure in this
galaxy a radio core with 132 mJy at 3.6 cm, and Nagar et al. (2002) obtained 165
mJy at 2 cm with the VLBA.
M81 was imaged by M05 at five epochs. The mean level at 2500 A, 200 *
10^-17^ erg cm^-2^ s^-1^ A^-1^, was similar to the one measured by Maoz et al.
(1998) at 1500 A in the 1993 HST/FOS spectrum of Ho, Filippenko & Sargent (1996)
- 150 * 10^-17^ erg cm^-2^ s^-1^ A^-1^. [From an analysis of the FOS target
acquisition records, Maoz et al. (1998) deduced that M81 was located at the
edges of its peak-up scans, possibly leading to some light loss.] The flux level
measured by M05 is also the same as the 2200-A flux estimated by Maoz et al.
(1998) by extrapolating the 1996 Wide Field Planetary Camera 2 (WFPC2)
measurement at -1600 A by Devereux, Ford & Jacoby (1997). The mean 3300-A flux
found by M05 was 130 * 0.11 * 10^-17^ erg cm^-2^ s^-1^ A^-1^. Variations
measured by M05 in both F250W (8 per cent) and F330W (11 per cent) give a lower
limits on the AGN flux of 200 * 0.08 * 10^-17^ and 130 * 0.11 * 10^-17^ erg
cm^-2 ^ s^-1^ A^-1^, respectively.
Ho et al. (2001) measured with Chandra an unabsorbed 2-10 keV flux from the
nucleus of 1.0 * 10^-11^ erg cm^-2^ s^-1^. Because the nuclear source was
heavily piled up, the counts were estimated from the readout trail.
A central BH mass of 6 * 10^7^ M_sun_ has been reported by Bower et al.
(2000) based on stellar kinematics, and 7 * 10^7^ M_sun_ by Devereux et al.
(2003) based on gas kinematics. I adopt the mean of the two.

10. 2007ApJS..173..538T
Re:NGC 3031
NGC 3031 (Fig. 16.11).-The primary member among one of the most well-studied
interacting galaxy groups, this SA(s)ab; LINER Seyfert 1.8 object has extensive
tidal arms apparent in the H I distribution (Yun et al. 1994, 2000). GALEX
observations show that the tidal arms host SF at a level greater than
appreciated via the H{alpha} tracer (comparing to the emission line image of
Greenawalt 1998). SDSS imaging reveals some of the XUV-disk cluster complexes in
NGC 3031. Within the large-scale tidal features, molecular gas has been found
(Brouillet et al. 1992; Braine et al. 2001). Tidal dwarf galaxies (van Driel et
al. 1998; Boyce et al. 2001; Makarova et al. 2002), isolated H II regions (Flynn
et al. 1998), and a diffuse stellar population (Sun et al. 2005) were previously
known to exist within the H I streamers. MUV and FUV imagery of NGC 3031 from
UIT (Hill et al. 1992; Marcum et al. 2001) illustrated a red bulge and blue SF
arms, but not the XUV-disk complexes.

11. 2007AJ....134..648M
Re:NGC 3031
NGC 3031 (M81; Figs. 7.19, 9.19, 20.19): This is the largest galaxy of one of
the nearest groups. It is a typical Sa type, with a big bulge that fills the
whole field of view of the camera. Some dust lanes are seen in the inner region,
although no young star clusters are clearly visible in the UV image. Ho et al.
(1995) describe it as a LINER.

12. 2007A&A...461.1209D
M81: Pellegrini et al. (2000) published these BeppoSAX data. Unlike
these authors, I also tested the addition of a reflection component that
is only marginally significant, yielding to an upper limit (R<=1.56) on
the amount of this component and a lower limit on E_c_ >= 96 keV. As
previously noticed by Pellegrini et al. (2000), the FeK{alpha} line is
only marginally consistent with being produced by cold matter (E = 6.7
+/- 0.1 keV). From the present analysis it is not clear what the site of
production of this component could be. Here, in fact, the absorption
edge detected at E~8.5 keV by Pellegrin i et al. (2000) is not measured
because of the addition of the reflection component. Thus, it is not
possible to exclude that the ionized FeK{alpha} line comes from an
ionized reflector or from a warm absorber.

13. 2006MNRAS.366.1265B
Re:NGC 3031
The great M81 spiral galaxy has few H{alpha} emission in its centre, given its
somewhat early type (Sab). The velocity information for radii up to ~4 arcmin is
thus difficult to extract. Farther away from the centre, the rotation curve is
very flat and does not show any decrease near the edge of the optical disc.
Long-slit observations performed by Pellet & Simien (1982) show the same
flattening. The bright core, as seen in IR, contrasts greatly with its dim
H{alpha} counterpart. Detailed investigation of the UV, H{alpha} and IR SFR
indicators based on Spitzer and SINGS ancillary data has been done by Gordon et
al. (2004) and suggests that the central dust is heated by stars in the bulge
rather than star formation. The morphological analysis of the IR data has been
done by Willner et al. (2004), and shows evolved stars organized in bulge and
disc components, a dusty ISM showing star-forming regions and a clumpy profile.
Still, according to Willner et al., the flux density of the point-like nucleus
seems to have decreased by a factor of 3 in the past 4 yr.

14. 2005ApJS..157...59L
Re:NGC 3031
NGC 3031 (M81) is an Sc spiral galaxy at a distance of 3.42 Mpc. ULX1 and ULX2
are both on a thin spiral arm. ULX1 is identified with SN 1993J. ULX2 is
identified as a black hole binary system with an O8 V secondary based on Chandra
and HST WFPC2 observations (Liu et al. 2002a).

15. 2005ApJ...627..674A
NGC 3031.This galaxy is more commonly known as M81. The compact VLBA core
contains virtually all of the radio flux seen on VLA scales. Bietenholz et al.
(1996, 2000) use these observations to measure the size of the emission region
of NGC 3031, finding a mean result of 530 +/- 100 microas x 180 +/- 40 microas
(at P.A. 50^deg^) at 8.4 GHz for their single-component model. (The
two-component model is very similar.) This measurement suggests a brightness
temperature of about 10^10.3^ K. Given the factor of 5 uncertainty in any
individual galaxy, our interstellar scintillation angular size result of about
100 microas is in remarkably good agreement with their findings. If some
fraction of the variability of NGC 3031 is intrinsic to the source, this would
increase the interstellar scattering size estimate, bringing our value into
even closer agreement with Bietenholz et al. This nearby (3.55 Mpc; Freedman et
al. 2001) galaxy has been known to contain a compact, variable radio nucleus
for many years. Crane et al. (1976) and de Bruyn et al. (1976) present radio
measurements from 1967 to 1975 showing that NGC 3031 had varied by up to a
factor of ~2 over that time. Following the SN 1993J explosion, the nucleus of
NGC 3031 was repeatedly observed as part of the SN 1993J monitoring campaign,
as it was located within the primary beam area of the VLA and VLBA telescopes
targeting SN 1993J. Ho et al. (1999, hereafter H99) present flux densities for
NGC 3031 at 1.4, 4.9, 8.4, and 15.2 GHz starting 3 days after the supernova
explosion and extending to almost 1400 days after the explosion. Since the
supernova is located about 170" away from the nucleus, there is no problem with
confusion. However, changing array configurations, uncertainty in the flux
density calibrations (CSOs were generally not observed), and other problems
cause the uncertainty levels in the individual me asurements to be far higher
than the measurements presented in this work. Variability statistics are
presented in Table 10; a P_{chi}^2^_ analysis gives a probability of only
10^-13^ that the nuclear emission was constant. The 8.4 GHz radio light curves
in H99 suggest that NGC 3031 has periodic "outbursts" that can double the
emission levels, separated by periods of relative "quiet." The high scatter in
Table 10 reflects the strong outburst periods.

16. 2005ApJ...627..674A
Re:NGC 3031
The observations of NGC 3031 presented in this work show far lower variability
levels but are consistent with the quiet period scatter levels. Assuming that
the variability in H99 is intrinsic, the brightness temperature limits are
higher than the values in Table 7 but still consistent with inverse Compton
limits. The 90% confidence estimate to the brightness temperature lower limit
is actually consistent with the equipartition brightness temperature limit of
~10^11^ K. Figure 14 shows structure function plots for the H99 data. The 1.4
and 4.9 GHz data show no significant intraday variability. The 8.4 GHz data
show significant variability down to ~0.5 days. If the 8.4 GHz data are
interpreted in terms of interstellar scintillation, the source angular size
predictions from both the initial maximum in the structure function and the
debiased measurement scatter are about 12 microas at 8.4 GHz. However, we agree
with the conclusion by H99 that the large amplitude variations seen in their
data are almost certainly intrinsic to NGC 3031, as the "outbursts" are visible
in all frequencies and are nearly coincident in time. Furthermore, the flux
density measurements of SN 1993J, only 170" away, show no evidence for large
amplitude fluctuations over a period of almost 4 yr. We find it very unlikely
that any phase screen covering NGC 3031 for this time period would never affect
the supernova emission as well. However, the cause of the few percent, quiet
intraday variability detected in this work could still be either intrinsic or
extrinsic to the source itself.

17. 2003ApJ...598..827P
Re:NGC 3031
NGC 3031 (M8]).-NGC 3031 shows a dramatic transformation between its
optical and UV morphology. Furthermore, this galaxy has some of the
largest {xi}-values of the sample. As illustrated by the color-residual
images for this galaxy in Figure 2, the large internal color dispersion
values apparently result from differences in the stellar populations
that constitute the bulge, disk, and star-forming spiral arms. It is
also notable that this galaxy is the only sample member with high
internal color dispersion between the FUV and MUV colors, i.e.,
{xi}(FUV, MUV) > 0.2. This galaxy (along with NGC 3034) is the nearest
galaxy in the sample (at a distance of 3.4 Mpc; Freedman et al. 2001),
and therefore one could postulate that the higher resolution available
for this galaxy somehow increases the internal color
dispersion. However, our simulations of NGC 3031 with poorer resolution
indicate that the resolution is not a dominant effect (see section
5). Therefore, in order to account for the high internal color
dispersion, the (older) stellar populations of the bulge must contribute
strongly to the flux in MUV wavelengths (with very little accompanying
FUV emission), whereas the FUV flux predominantly stems from young
star-forming complexes in the spiral arms. NGC 3031 beautifully
illustrates how differences in the composition of the stellar
populations that make up each galaxy component (i.e., the bulge, disk,
spiral arms) can generate large internal color dispersion.

18. 2002MNRAS.329..877C
Re:GB6 J0955+6903
50-redshift from de Vaucouleurs et al. (1991); LINER, Sy1.8

19. 2002ApJS..139....1T
Re:NGC 3031
NGC 3031 (S1.5).-ASCA observed this galaxy many times; see Iyomoto &
Makishima (2001), who analyzed 16 data sets, for the observation log and
a timing analysis. Ishisaki et al. (1996) presented detailed results
of the observations between 1993 May 1 to 1995 April 1, while
Serlemitsos et al. (1996) describe three observations done on 1993 April
16, April 25, and May 1.
We present a combined spectrum of the three observations performed
on 1994 October 21, 1995 April 1, and 1995 October 24 (observations 9,
10, and 11 in lyomoto & Makishima 2001). More recent observations were
made using unusual observation modes (lower spectral and spatial
resolution but higher timing resolution for GIS). In the earlier
observations, the nearby source SN 1993J was bright, and we therefore
omitted these in the present analysis.
In our spectral fits, we discarded the energy range below 1 keV
for the SIS data since the spectra of the SIS and GIS deviate in this
energy range, most likely because of a calibration problem of the SIS
in the soft-energy band. This problem is visible only in bright objects
such as NGC 3031, and possibly NGC 4579 and NGC 5033.
A soft thermal component is not clearly seen in our spectra
presumably due to the brighter hard component in our spectrum, and we
assumed the temperature obtained by Ishisaki et al. (1996). The width
of the Gaussian component for the Fe line was assumed to be narrow
since the line width was not well constrained. The broad ({sigma} 0.2
keV) or possibly multiple-component Fe line previously reported by
Ishisaki et al. (1996) and Serlemitsos et al. (1996) is not clearly
seen in our spectra, presumably due to the limited photon statistics.
The BeppoSAX observation of Pellegrini et al. (2000b) gave upper limits
of 0.3 keV for the width of an Fe line. The line centroid energy and EW
we obtained are consistent with the ASCA results by Ishisaki et al.
(1996) and Serlemitsos et al. (1996) and the BeppoSAXresults of
Pellegrini et al. (2000b). Pellegrini et al. (2000b) obtained an upper
limit of 42 eV for the EW of an Fe line at 6.4 keV.

20. 2002ApJ...574..740T
Re:NGC 3031
NGC 4594 (Kormendy et al. 1996b), NGC 4486B (Kormendy et al. 1997),
NGC 4350 (Pignatelli, Salucci, & Danese 2001), NGC 3031 = M81, and
NGC 3998 (Bower et al. 2000) exhibit strong evidence from stellar
dynamics for a black hole but do not yet have three-integral dynamical

21. 2002AJ....124..675C
Re:UGC 05318
M81. Flux density from Condon (1987).

22. 2002A&A...388...50F
Re:NGC 3031
HST H{alpha} imaging reveals the presence of a nuclear gaseous
disk (Dereveux et al. 1997) similar in size and shape to the
CNKD of M 87 (see Macchetto et al. 1997 and references therein).
The disk is rotating around a SMBH with
M_black hole_ = 3 x 10^6^ M_sun_, according to determinations
based on stellar kinematics (Bower et al. 1996) and broad-line
emission (Ho et al. 1996). The spatial and spectral resolution
of our spectrum allow us only to detect the presence of a broad
and bright central component in the PV diagram. In fact, it
exhibits the highest central-to-outer integrated-flux ratio of
our sample, which warrants a Type III classification. From the
available spectrum, it is difficult to claim that NGC 3031 is
hosting a CNKD even though we measure a remarkably large
({DELTA}V/{DELTA}r)_in_ (=3.4 km s^-1^pc^-1^) and a large
inner-to-outer velocity-gradient ratio ({GAMMA}=3.0).

23. 2001ApJS..133...77H
Re:NGC 3031
NGC 3031, M81 (S1.5). - The nucleus of M81 contains a bright (~90 mJy),
variable, flat-spectrum radio core (e.g., Crane, Giuffrida, & Carlson 1976;
de Bruyn et al. 1976; Bartel et al. 1982) with a one-sided jet on VLBI
scales (Bietenholz, Bartel, & Rupen 2000). Its variability pattern is
complex, with occasional outbursts during which the source doubles in
brightness at higher frequencies (Ho et al. 1999b). The multiconfiguration
study by Kaufman et al. (1996) reveals a wealth of structural details. We
reprocessed their 6 cm B array and 20 cm A array data, and most of the
morphological features discussed by Kaufman et al. are recovered in our
maps. The most spectacular feature is an arclike structure located 45" to
the northeast of the nucleus at P.A. ~ 45^deg^, highly suggestive of an
outflow origin. There are, in addition, a number of compact sources located
within the central ~2' which are likely to be associated with M81 (see
Kaufman et al. 1996 for details). In deriving the largest linear extent of
the source, we do not include the two compact sources labeled "57" and "75"
in Figure 6 of Kaufman et al. (1996); their relation to the nucleus, though
suggestive, is uncertain. Kaufman et al. (1996) have discussed extensively
the polarization measurements of M81. Here we only remark that we have
largely recovered the polarization structure found by Kaufman et al., the
most notable feature being the high degree of polarization along the arc
at 20 cm (Fig. 16d). At 6 cm, in addition to the weak polarized emission
near the core reported by Kaufman et al., we also find some polarized
signal associated with the arc; the polarization fraction approaches 100%
in some locations along the arc. This very high value could be partly
caused by resolving out much of the extended total-intensity emission,
with the polarization changing on somewhat smaller scales to which the
interferometers are more sensitive.

24. 2001ApJS..132..129M
Re:NGC 3031
NGC 3031 (M81). - At a distance of ~3.6 Mpc and having large angular
size (14' x 26'), the grand design SA(s)ab spiral galaxy M81 is
morphologically similar to M31 and has often been used as a test of density
wave theories (e.g., Adler & Westphal 1996). FOCA images of M81 at 2000 A
with resolution ~20" have been analyzed by Blecha et al. (1990) and Reichen
et al. (1994), who compared the UV continuum in detail to other tracers of
spiral structure, including H{alpha}, H I, and free-free radio emission.
A preliminary discussion of the UIT images (Fig. 17a) was given by
Hill et al. (1992b). In the FUV, the bulge is very faint, and its surface
brightness drops precipitously with radius, by 5.5 mag within 50",
exhibiting a 2.5 mag increase in the (FUV-MUV) color (Fig. 17b). In both
the MUV and FUV bands, the bulge follows a de Vaucouleurs r^0.25^ profile
within r <~ 50". M81 contains a low-luminosity LINER/Seyfert 1 active
nucleus. This AGN is not detectable in the UV at our 3" resolution, and our
FUV profile shows no evidence of a nuclear point source. However, the
active nucleus was recently detected in the UV with HST (Ho, Filippenko,
& Sargent 1996; Devereux, Ford, & Jacoby 1997) as a faint point source
(d <~ 0.04") which photoionizes a small gas disk extending to r ~ 7".
In both the FUV and MUV frames of Figure 17a, the galaxy has a
"ringlike" morphology, produced by the pattern of UV knots strung out along
the dominant spiral arms and the faintness of the central regions of the
galaxy out to r ~ 200". Not only do the outer parts of the bulge become
very faint in the FUV, but there is evidently little underlying disk light
inside 200". The inner edge of the disk near r ~ 250" also exhibits a large
(FUV-MUV) color gradient, evidence of a rapid change in the mean age of the
disk population. There are remarkable changes of morphology with
wavelength. Comparing the MUV to the R band, we see that the outer disk
becomes more prominent and structured at shorter wavelengths while the
central bulge is much less prominent (see Fig. 17a). The contrast between
the large UV color gradients and the tiny (B-R) gradient is striking in
Figure 17b. The (FUV-MUV) color is roughly uniform at radii larger than
300" in the disk. The (UV-V) colors in the disk are redder than those
observed in M33 and M74, indicating an older characteristic age for the
disk (Cornett et al. 1994). In the rest-frame FUV, a high-redshift galaxy
like M81 would not appear to be a normal spiral galaxy.
UV, H{alpha}, and extinction properties of the 52 brightest resolved
sources are discussed by (Hill et al. 1992b, 1995a). They estimate the
total mass in recently formed massive stars (5-120 M_sun_) to be
1.4 x 10^5^ M_sun_. The inferred star formation rate is 0.13 M_sun_ yr^-1^.
Allen et al. (1997) have compared the UIT images to H{alpha} and H I maps
of M81 at 9" resolution. They find that while bright H{alpha} peaks are
always associated with bright UV continuum peaks, the converse is not
always true, which is expected because the UV continuum persists for many
times the duration of strong photoionization. H I is closely associated
with the UV continuum, suggesting that it is a produced by stellar UV
photodissociation from a massive underlying H_2_ layer and is not a
precursor to star formation. Obscuration by dust has little effect on the
morphology of M81 (or most of the other normal galaxies in this atlas),
and Allen et al. (1997) argue that local chimneys blown in the dust layer
by concentrated star formation permit the UV light to escape with little

25. 2001AJ....121..710S
4.4. M81 and NGC 3077
The tidal features of M81 and NGC 3077 have also been detected in CO
(Brouillet et al. 1992; Walter & Heithausen 1999). Like those in
Arp 245 and NGC 3561, they also have high inferred M_H_2__/M_H I_
ratios (Table 6). However, the inferred H_2_ masses in the CO beam
are small (~10^6^ M_solar_, using the standard Galactic N_H_2__/I_CO_
ratio; 10^7^ M_solar_, using the virial theorem) and there is no
evidence for on-going star formation in these locations (Brouillet et
al. 1992; Henkel et al. 1993; Walter & Heithausen 1999). The
M81/M82/NGC 3077 group is very nearby, so the area subtended by the
CO beam (~360 pc) is much smaller than in the other systems listed.
The other features plotted in Figure 3 have physical beam diameters
ranging from 1.8 kpc (NGC 4438) to 43 kpc (I Zw 192). As with the
Arp 245 and NGC 3561 features, the CO self-shielding threshold may be
exceeded locally in these features. We note that the H I column
density in the CO beam is quite high for the M81 and NGC 3077
positions, 10^21^ cm^-2^.

26. 2001A&A...378...51B
M 81 - IMC 1 & 2: The first intergalactic molecular clouds (hence the
name IMC) were discovered by Brouillet et al. (1992) as part of the M 81
group tidal material. So far, no stellar emission has been detected from
this object (Henkel et al. 1993). A similar object was recently found by
Walter & Heithausen (1999) near NGC 3077 in the same group, again with
no sign of a stellar component. These objects may well be small
"future TDGs", using the definition of a TDG as containing a stellar
component. Like our sources, the molecular gas is found at the HI column
density peak and must have formed from the atomic gas.

27. 2001A&A...374..394V
Re:NGC 3031
NGC 3031: We measure the same V_*_ gradient as Bender et al. (1994) and
Heraudeau & Simien (1998) in the inner |r| <~ 10". Further out our V_*_
continues to increase. The differences between the three V_*_ sets are as
large as 50-80 km s^-1^. In the same radial region our {sigma}_*_ agrees
with the velocity dispersions by Bender et al. (1994) but are about
50 km s^-1^ lower than those by Heraudeau & Simien (1998). {sigma}_*_
measurements do coincide in the centre. These differences in V_*_ and
{sigma}_*_ are due to the different instrumental setup used for the
different observations. We used a very spatial resolution, so the velocity
gradient we measure is more accurate than that of the other authors. The
differences in the values of {sigma}_*_ between our measurements and those
obtained by Heraudeau & Simien (1998) are probably due to a template
mismatching effect.

28. 2001A&A...374..394V
Re:NGC 3031
NGC 3031: Sofue (1997) combined different optical and radio data sets to
trace gas rotation of this spiral galaxy out to more than 20'. There is no
evidence of kinematical decoupling between gas and stars even if our
higher-resolution data show that in the inner +/-1' the gas velocity curve
is highly disturbed and less regular than the stellar one.

29. 2001A&A...368..797P
Re:NGC 3031
NGC 3031: For NGC 3031 (M 81) we used the distance of 3.63 Mpc given in
Freedman et al. (1994) to compute the luminosity of this object (z < 0).

30. 2000MNRAS.319...17L
A 0951+68: This galaxy has been observed in X-rays for the first time. As
can be seen in Fig. 12, the only detected source is probably a foreground
or background object.

31. 2000MNRAS.319...17L
Re:NGC 3031
NGC 3031: No analysis of X-ray data for this galaxy has been done in this
paper. Nine and 30 point sources have been detected in this galaxy from
observations with the Einstein and ROSAT HRI, respectively (Fabbiano 1988;
Roberts & Warwick 2000). All Einstein sources within the galaxy D_25_
isophote were detected by ROSAT, with the exception of the Einstein source
X1. ROSAT sources located within the central ~6 x 6 arcmin^2^ region
are listed in Table 6.
The central emission is dominated by the nuclear source, coincident
with a low-luminosity active nucleus, with a luminosity <~ 10^40^ erg s^-1^
in the 0.2-4.0 keV bandpass. Einstein IPC data show that the spectrum of
the nuclear source is soft, with a good fit given by thermal emission with
kT ~ 1 keV or by a power law with index {alpha} ~ 2 (Fabbiano 1988).
Broad-band observations obtained with BBXRT (0.5-10 keV) and ASCA
(0.2-10 keV) show, however, that the nuclear emission is consistent with a
power-law distribution with index {alpha} ~ 1 (Petre et al. 1993;
Ishisaki et al. 1996; Serlemitsos, Ptak & Yaqoob 1996). The ASCA data also
revealed the presence of a broad iron K emission line similar to those seen
in more luminous Seyfert galaxies (Ishisaki et al. 1996; Serlemitsos et al.
1996). It must be kept in mind that, due to the coarse spatial resolution
of ASCA, some contamination is expected from nearby sources, although
(Ishisaki et al. 1996) estimated this to be less than 10 per cent. X-ray
long-term and fast variability by significant factors have been reported
for the nuclear source (Petre et al. 1993; Ishisaki et al. 1996;
Serlemitsos et al. 1996).

32. 2000ApJ...530..688A
Re:NGC 3031
NGC 3031 (M81).-The LINER M81 is one of the best candidates for
low-luminosity AGN (i.e., AGN-dominated LINER in our classification).
Its properties in the UV and optical have been recently studied in great
detail by Ho et al. (1996). Our J-band spectrum shows [Fe II] 1.257
micron emission embedded in a very strong underlying stellar continuum.
The [Fe II] emission must be very localized at the center of the galaxy,
since the off-nucleus spectrum (see Fig. 2) shows no emission from this
line. The Pa{beta} line is probably seen in absorption. Owing to the
radial velocity of this galaxy, a small error in the correction for the
Pa{beta} emission introduced by the division by the standard star can
affect the detection of a very faint Pa{beta} emission from M81.

33. 1999ApJ...519...89C
Re:NGC 3031
NGC 3031 (M81).-This galaxy is described as having a LINER nuclear
spectrum (Heckman 1980); some nuclei classified as LINERs are
low-luminosity AGNs (e.g., Ho et al. 1995, hereafter HFS95). Petre et
al. (1993) describe its X-ray spectrum as being similar to that of other
LINERs with broad H{alpha} emission but argue against the presence of
an accretion disk. Ishisaki et al. (1996) argue for the presence of a
low-luminosity AGN in M81, based on the results from eight ASCA

34. 1998AJ....116.2682C
Re:IRAS 09514+6918
M81, NGC 3031. Seyfert 1.5.

35. 1997AstL...23..656G
M 81. We estimated the magnitude V(5) using the photographic data of Sandage
(1984a), Zickgraf and Humphreys ([991), and Georgiev et al. (1992a, l992b).
Perelmuter and Racine (1995) provide the color-magnitude diagrun for a region
of M 81, whose area is approximately a factor of 10 greater than the area of
the galaxy. Because of the large contribution of field stars, the magnitude V(5)
estimated from these data appears to be more than 0.2^m^ brighter than our

36. 1997AstL...23..644G
M 81. Freedman et al. (1994a) (Cepheids); Georgiev et al. (1992a, 1992b); (nos.
16, 23, 14), (nos. 263, 26, 90). The photographic magnitudes and colors of the
blue stars were reduced to the CCD scale of Metcalfe and Shanks (1991) by
subtracting 0.11^m^ and 0.32^m^, respectively. The selected candidates for the
brightest red supergiants turn out to be brightest in the sample under
consideration, whereas the red stars that were identified by Sandage (1984a)
[Humphreys et al. (1987) spectroscopically proved that they were red
supergiants] are 1^m^ fainter. Note that Georgiev et al. (1992a, 1 992b)
detected about ten candidates for red supergiants which show up in M 81
immediately after 19^m^. Nevertheless, the selection of the brightest stars is
unreliable in this case.

37. 1997ApJS..112..391H
Re:NGC 3031
NGC 3031.--As was first discovered by Peimbert & Torres-Peimbert (1981),
confirmed by Shuder & Osterbrock (1981), and subsequently studied in greater
detail by Filippenko & Sargent (1988), NGC 3031 (M81) has a conspicuous
(f_blend_~57%) broad H{alpha} line with FWHM~2650 km s^-1^. The recent
detections of nonthermal X-ray emission (Petre et al. 1993; Ishisaki et al.
1996), a highly compact VLBI radio core (Bietenholz et al. 1996), and a
nonstellar, featureless ultraviolet continuum (Ho et al. 1996) have made
NGC 3031 the first LINER whose multiwavelength spectrum has been studied in
depth. The narrow-line spectrum is characterized by a large range of line
widths because of density stratification (Filippenko & Sargent 1988; Ho et
al. 1996). Although a model of [S II] {lambda}6731 roughly matches [N II]
and narrow H{alpha} (see, e.g., Filippenko & Sargent 1988 and Fig. 9e), it
is obvious from the residuals that the base of [N II] is somewhat wider than
that of [S II]. Moreover, the two [S II] lines clearly have different widths
(Filippenko & Sargent 1988; Fig. 1b). The dominance of the broad H{alpha}
component makes it difficult to derive the true profile parameters of [N II].
Both H{beta} and H{gamma} have broad components (see also Filippenko & Sargent
1988), and spectra taken with the Hubble Space Telescope (HST) show several
additional broad lines in the ultraviolet (Ho et al. 1996).

38. 1997A&A...319...33A
Re:NGC 3031
NGC 3031 This Seyfert, M81, and the preceding Seyfert, Cen A, are so much
closer in distance to us that the typical pairs evident around more distant
Seyferts would be outside the field of the PSPC. This means that many of the
sources are within the optical confines of the galaxy and, as Fig. 1b of
Radecke shows, represent normal objects such as X-ray binaries and supernovae.
Therefore we leave the discussion of the bulk of these sources to detailed
analyses, e.g. in M81 to Fabbiano (1988) and Zimmerman (1996, in preparation).
For sources comparable in strength and separation to those shown in Figs. 2-13
it would be necessary to analyze ROSAT Survey fields. But we can mention three
aspects of M81:
1) A source C=12.5, at 6.1'N is paired with a source C=68.7, 33.4'S. Both show
radio emission and are optically identified with respectively, a stellar object
and an HII region (Fabbiano 1988). They should be investigated
2) M82, lying 37'N of the nucleus of M81 is a very srong X-ray source (C=815).
It is well known that this is an early spectral type, starburst galaxy with an
excess redshift with respect to M81 of {DELTA}cz = +286 kms^-1^ (Arp 1994b).
In the following analyses of Seyfert neighborhoods we will see a number of
examples of smaller companions in active phases with varying degrees of excess
3) There is a strong source, C=148, about 12'E of the nucleus of M81. It lies
near the edge of the dwarf galaxy Holmberg IX. The X-ray position falls close
to a faint blue, partly nebulous object which should be checked
spectroscopically. If this source is not a faint, powerful X-ray AGN then its
nature is even more mysterious. (see Table 2 at end.)

39. 1995ApJS...98..477H
Re:NGC 3031
(M81) Filippenko & Sargent (1988) describe in detail the emission-line
properties of this well-studied LINER. Among the characteristics which
qualify M81 as one of the best low-luminosity AGN candidates include a
broad H{alpha} component (full width near zero intensity ~ 7000 km s^-1^)
with a luminosity ~ 20 times smaller than that of the faintest
``classical'' Seyfert 1 galaxy (NGC 4051, Veron 1979), a compact radio
core (Kellermann et al 1976), a point-like X-ray source as seen by ROSAT
(Petre et al 1993), and rapid X-ray variability (Barr et al 1985).

40. 1994CAG1..B...0000S
Re:NGC 3031
M81 Group
Hubble Atlas, p. 19
April 15/16, 1952
30 min
NGC 3031 is the type example of a large-bulge, regular,
thin-armed Sb galaxy of the Andromeda Nebula (M31) type but with
thinner, more regular arms. Dust lanes thread through the central
bulge. The lanes can be traced close to the nucleus, as in M31, but
are not seen in this print because of the overexposed central region.
The luminous arms cannot be traced as single grand design
structures, but rather as spiral fragments that branch into many
secondary filaments. The dust is generally on the inside of the
The spiral arms are highly resolved into stars beginning at
apparent magnitude B = 18. Normal novae, Cepheid variables, and
planetary nebulae have also been identified in the resolved stellar
content. The distance modulus is m - M = 27.7, based on the resolution
and identification of these distance indicators, in particular the
Cepheid variables.
M81 is the brightest member of the M81/NGC 2403 extended g1roup
(Holmberg 1950), which includes NGC 2266, NGC 2976, NGC 3077, NGC
4236, IC 2574, M82, Ho I, Ho II, Ho IX, and a number of dE dwarf
ellipticals (Kraan-Korteweg and Tammann 1979; Borngen and
Karachentseva 1982; Borngen, Karachentseva, and Karachentsev 1984;
Borngen, Karachentseva et al. 1982).
An intricate pattern of straight dust lanes exists, not connected
wit1h the spiral structure, across the central disk (bulge) and across
the brighter spiral arm on the north-preceding side (lower right),
seen particularly well in the insert. These lanes may be dust in the
halo of our galaxy connected with the high-latitude nebulosities that
are prevalent in the direction of the M81/M82 pair (Sandage 1976,
Plate VI).

41. 1993ApJS...86....5K
Re:NGC 3031
NGC 3031 (M81); Sb, LINER.
M 81 is a nearby Sb galaxy, which has the low-ionization emission lines
of a LINER (Heckman 1980) but also has the broad emission lines of a
low-luminosity Seyfert 1 galaxy (Peimbert & Torres-Peimbert 1981). The
galaxy contains a compact, powerful nuclear radio source (Condon et al.
1982; Kellermann et al. 1976). Keel et al. (1985) have found evidence
that tidal interactions with companions increase the activity of the
nucleus. M 81 appears to be interacting with the other components of the
M 81 group, which show a common H I envelope (Condon et al. 1982).
The spectra of M 81 include only those with the aperture centered on
the galaxy (cf. Peimbert & Torres-Peimbert 1981; Ellis, Gondhalekar, &
Efstathion 1982). The UV spectrum has been analyzed by Peimbert & Torres-
Peimbert (1981) and by Ellis et al. (1982). The emission probably
originates from two different regions: The narrow permitted lines and the
forbidden lines, on the one hand, come from an extended region where gas
is shock-heated by a central source or photoionized by a power-law
spectrum. The broad permitted lines, on the other hand, originate in a
small, compact central region. The line broadening is due to the motion
of the gas around a very compact central object (M ~ 10^7^ M_sun_;
Peimbert & Torres-Peimbert 1981; see also the detailed analysis of
Filippenko & Sargent 1988). In spite of the presence of the typically
broad Seyfert emission lines, such as Mg II {lambda}2800, the UV
continuum is that of a normal early-type spiral galaxy.

42. 1976RC2...C...0000d
Re:NGC 3031
= Messier 081
= Kara[72] 218a
Description: (Outer ring feature)
Science, 148, 363, 1965.
Sov. A.J., 10, 1057, 1967.
Sov. A.J., 12, 715, 1969.
Description: (Faint Companion) (See A0953+69 = DDO 066 = Holmberg IX)
Astr. Ap., 32, 117, 1974
P.A.S.P., 84, 61, 1972.
Science, 148, 363, 1965.
A.J., 72, 1032, 1967.
P.A.S.P., 79, 600, 1967.
Ap. J.Suppl., 24, No. 210, 1972.
Astr. Ap., 29, 231, 1973.
Photometry: (12 Color)
Ap. J., 145, 36, 1966.
Photometry: (5 Color)
A.J., 73, 313, 1968.
Photometry: (UBV)
Ap. J., 157, 55, 1969.
Surface Photometry and Isophotometry:
A.J., 72, 1032, 1967.
Astrofizika, 7, 407, 1971.
Ap. J. Suppl., 24, No. 210, 1972.
Ap. J., 192, 311, 1974.
Bull. A.A.S., 4, 224, 1972.
Bull. A.A.S., 5, 448, 1973.
Photometry: (I.R.: 1.64 microns)
Sov. A.J., 12, 184, 1968.
Astr. Ap., 9, 45, 1970.
Internal Motions:
Ap. J., 192, 311, 1974.
Bull. A.A.S., 4, 332, 1972.
Observatory, 88, 239, 1968.
Ap. J., 154, 33, 1968.
Ap. J. Suppl., 22, No. 193, 1971.
Ap. J., 178, 617, 1972. 186, 21, 1973.
A.J., 74, 150, 1969.
C.R. Acad. Sc., Paris, (B), 268, 1397, 1969.
Bol. Tonantzintla, 6, No. 37, 97, 1971.
Astr. Ap., 9, 45, 1970.
Astr. Ap., 10, 401, 1971.
Astr. Ap., 19, 405, 1972.
Astr. Ap., 20, 361, 1972.
Astr. Ap., 27, 433, 1973.
Astr. Ap., 37, 57, 1974.
Astrophys. Lett., 14, 1, 1973.
IAU Symp. No. 44, 55, 188, 1972.
IAU Symp. No. 58, 169, 1974.
Molecular Absorption Lines: (H2O, CO)
Astrophys. Lett., 14, 1, 1973.
A.J., 72, 784, 1967.
P.A.S.P., 79, 600, 1967.
"Nuclei of Galaxies", 195, 1971.
Dynamics, Rotation Curve and Mass Determination:
Astr. Ap., 8, 364, 1970.
Ap. J. Suppl., 24, No. 210, 1972.
Ap. J., 184, 735, 1973.
Ap. J., 192, 311, 1974.
Bull. A.A.S., 6, 212, 1974.
HII Regions:
P.A.S.P., 83, 61, 1972.
HI 21cm:
Astr. Ap., 26, 483, 1973.
Astr. Ap., 31, 245, 1974.
IAU Symp. No. 44, 12, 1972.
IAU Symp. No. 58, 120, 1974.
Proc. 1st Europ. Astr. Meet., Vol. 3, 15, 1974.
Bull. A.A.S., 6, 435, 1974.
Radio Observations:
Ap. J., 142, 1333, 1965.
A.J., 73, 876, 1968.
Astr. Ap., 29, 231, 1973.
IAU Symp. No. 58, 377, 1974.
Proc. 1st Europ. Astr. Meet., Vol. 3, 1, 1974.
X-Rays in M81-M82 Group:
Bull. A.A.S., 3, 398, 1971.

43. 1973UGC...C...0000N
Re:UGC 05318
SA(s)ab (de Vaucouleurs), Sb- (Holmberg)
UGC 05336 (Holmberg IX = DDO 66) at 10.8, 95
UGC 05322 (= M 82) at 37.
UGC 05398 at 46.5

44. 1964RC1...C...0000d
Re:NGC 3031
= Messier 081
Slow decrease of (B-V) with log A/D(0), interpolated value.
Ap. J., 32, 34, 1910.
Ap. J., 92, 22, 1940.
Ritchey, L'Evolution de l'Astrophotographie ...,
Soc. Ast. de France, Paris, 1929.
P.A.S.P., 71, 102, 1959.
P.A.S.P., 71, 534, 1959.
Handbuch der Ap., 5, 2, 843, 1933.
Ap. J., 46, 206, 1917.
Ap. J., 50, 384, 1919.
Ap. J., 83, 434, 1936.
Ap. J., 91, 528, 1940.
M.N.R.A.S., 94, 806, 1934.
Medd. Lund II, 128, 1950.
Dennison, Univ. of Michigan Thesis, 1954.
Sov. A.J., 32, 16, 1955.
Izv. Pulkovo, 20, No 156, 87, 1956.
P.A.S.P., 71, 102, 1959.
Lick Obs. Bull. 497, 1939.
Ap. J., 135, 733, 1962.
Ap. J., 104, 221, 1946.
P.A.S.P., 71, 534, 1959.
Ap. J., 97, 117, 1943.
A.J. 62, 28, 1957.
P.A.S.P., 71, 102, 1959.
Bull. Abastumani. No. 18, 15, 1955.
HII Regions:
Observatory, 79, 54, 1959.
Zeit. fur Ap., 50, 168, 1960.
Radio Emission:
Nature, 172, 853, 1953.
M.N.R.A.S., 122, 479, 1961.
Ap. J., 134, 659, 1961.
Handbuch der Phys., 53, 253, 1959.
HI Emission:
Ap. J., 126, 471, 1957.
P.A.S.P., 72, 368, 1960.
B.A.N., 15, 307, 1961.
NOVA 1950,
P.A.S.P., 62, 116, 1950.

45. 1961Hubbl.B...0000S
Re:NGC 3031
Apr. 15/16, 1952
30 min
Enlarged 3.0X
M81 has a large amorphous central region in which there
is no suggestion of resolution into individual stars. There
is no doubt that this region resembles the central part of
M31 and that, under the proper conditions, with a large
telescope, M81 could be resolved into stars just as Baade
resolved M31. The distance modulus of M81 is about
(m-M) = 27.1 (Sandage, A. J., 59, 180, 1954). If Mv = -3.0
for the brightest stars in the central lens, then mv = 24.1.
This is beyond the limits of the 200-inch telescope
with the Ross f/3.67 lens. Two possibilities exist,
however, for achieving the resolution of M81. We can use the
f/4.85 lens, which will give about a one-magnitude increase
in the limit, and we can go to the infrared where the
absolute magnitude for these globular-cluster-like stars is
undoubtedly brighter than -3.0.
Dust lanes, forming a multiple spiral pattern, thread
through the central region and are silhouetted against the
amorphous, luminous background. These fainter multiple
dust lanes do not show in the illustration because of
the overexposed central region. They can be traced to
within 35 sec of arc from the center (8 mm on this
illustration) along the major axis.
The outer dust lanes lie on the inside of the luminous
spiral arms. These arms are thin, moderately well defined,
and branched near the ends of the major axis. Note the
intricate dust pattern at the south-following (southeast)
end of the major axis. There is an even more intricate
pattern of straight dust lanes, which has no connection
with the spiral structure, on the north-preceding end of
the major axis. The parallel streaks can be traced across
the central lens and across two branches of the brighter
spiral arm on the north-preceding side.
The arms are highly resolved into individual stars and
HII regions. The stellar contents of M81 are similar to
the contents of M31. Twenty-five normal novae have been
found; three variables which are definitely cepheids,
fifteen other variables which are probably cepheids, seven
irregular blue variables of the type known in M31 and
M33, and a number of irregular red variables are known.
All these stars are brighter than M(pg) = -4.5.

46. 1961AJ.....66..541B
Re:NGC 3031
2. NGC 3031 Group
The four bright galaxies in this group are NGC 2976, 3031, 3034, and 3077, and
there are fainter members also. Holmberg (1952) discussed a way of obtaining the
mass of NGC 3031 from motions of its satellites; this is in reasonable agreement
with the value of about 1.5X 10^11^ M_sun_ obtained from its rotation. A mass of
about 1.5 X 10^10^ M_sun_ is estimated for the mass of NGC 3034 from its
rotation. Ambartsumian (1958) argued that the system as a whole could not be
stable because of the large velocity (338 km/sec) of NGC 3034 relative to the
rest of the group.

47. 1956AJ.....61...97H
Re:NGC 3031
HMS Note No. 071
Plates by H. W. Babcock:
that of April 02.8 was taken with the slit on the minor axis.

48. 1918PLicO..13....9C
Re:NGC 3031
Vol. VIII, Plate 21; M.81. This very beautiful spiral is about 16' x 10', and
is too well known to require description. Short exposures show that the
nucleus is almost stellar. Central part very bright. See Abs. Eff. 10 s.n.

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