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Notes for object MESSIER 101

28 note(s) found in NED.

1. 2009ApJ...697.1870E
Re:NGC 5457
NGC 5457 (M 101) We measured 10 offsets at r = 1.7-3.1 kpc (0.8'-1.5'). Although
the data range in {OMEGA} is rather narrow, we were able to derive t_SF_ and
{OMEGA}_P_. We should note that the region where we measured offsets is only the
central part of the whole disk, whose R_25_ is 11.9'.
Cedres & Cepa (2002) derived the H{alpha} equivalent width from
observations with narrow band filters, and estimated a mean age of H II regions
at r <~ 5' to be about 1.6-4 Myr, supporting our result of t_SF_ = 4.0 +/- 1.3
The fitted {OMEGA}_P_ of 72 +/- 37 km s^-1^ kpc^-1^ locates the
corotation at R_CR_ = 2.7^+3.7^_-0.9_ kpc, or 1.3^+1.8^_-0.4_ arcmin. Waller et
al. (1997) derived {OMEGA}_P_ = 19 +/- 5 km s^-1^ kpc^-1^ using offsets between
CO and far-ultraviolet (FUV) at r ~ 1.5', assuming the timescale from CO to
FUV to be 3 Myr, locating in R_CR_ = 5.5' +/- 1.5'. Elmegreen et al.
(1992) also located the corotation at 5.5' from the optical appearance.
This discrepancy in R_CR_ implies a radial variance of the pattern speed or the
inclination angle, which could be caused by interactions with companions, NGC
5474 and NGC 5477. If the inner disk, where we measured offsets, is more
inclined than the adopted inclination angle of 18^deg^, the resultant
{OMEGA}_P_ would be smaller or closer to other results mentioned above than the
value presented here. In terms of the inclination, the adopted value for this
galaxy is one of the smallest in our sample, implying a difficulty in deriving
RC, which could be also inferred by the poor consistency in available RCs (see
Figure 3). The uncertainties derived by the fitting, thus, could be

2. 2007MNRAS.382.1552L
Re:NGC 5457
NGC 5457 - M 101: Fig. 2 shows that the central region contains three bright
sources, the northernmost of which corresponds to the nucleus (source 1). All
the sources have H{alpha} counterparts in the image of Moody et al. (1995). Dust
features appear as light patches in the image of the central kiloparsec. X-ray
observations with Chandra (Pence et al. 2001) show two nearly-identical nuclear
X-ray sources coincident with the nucleus and source 2. There is a weak extended
radio continuum source at the position of the nucleus (Turner & Ho 1994).
Spectra were obtained for these two sources. The spectrum of the nucleus shows
strong emission lines and absorption features from an underlying stellar
population. Source 2 shows the spectrum of a reddened starburst region and a
weak underlying stellar component. The very weak [O III] {lambda}5007 line and
strong [N II] and [S II] lines observed in both sources imply high

3. 2007ApJS..173..538T
Re:NGC 5457
NGC 5457 [M101] (Fig. 16.27).-This giant SAB(rs)cd galaxy dominates a group
having at least 8 members, including NGC 5474 and NGC 5477, with both of which
it is probably interacting. Our GALEX observations show a radial gradient in
FUV-NUV (Gil de Paz et al. 2007a), getting clearly bluer at large galactocentric
distances. Although discrete SF complexes do appear redder in the inner disk,
some of the central NUV flux originates in a diffuse slightly older stellar
population. This component gradually fades, leaving only the very blue,
prominent branching spiral arms at large galactocentric distance. Comparison
with SDSS imagery confirms that a wealth of filamentary UV-bright cluster
complexes in the outermost disk can be traced easily in the GALEX observation
(Bianchi et al. 2005), but only intermittently at optical wavelengths. The
previously unrecognized extent of recent star formation is greatest on the east
side of the galaxy, reaching most of the way to NGC 5477. Prior UV observations
of Waller et al. (1997) suggested that tidal interaction with companions and an
internal perturber (NGC 5471) have produced the kinked, linear morphology spiral
arms in M101. Low metallicity of the outer disk has been demonstrated by Garnett
& Kennicutt (1994) for the H II region H681. The H I distribution (Beale &
Davies 1969; Rogstad & Shostak 1971; van der Hulst & Sancisi 1988; Braun 1995)
is lopsided and conceivably distorted by tidal forces.

4. 2006A&A...452..739S
Re:NGC 5457
X9, X17, X26, and X29 in NGC 5457.
Also known as Messier 101, NGC 5457 is a nearby face-on Sc spiral galaxy within
a rich group. It is the prototype of the multiple-arm galaxies of the Sc
X9 and X17 appear projected against the spiral arms of the galactic disk (see
electronic Fig. 8). Extended emission around their proposed radio counterparts
is clearly detected. Therefore, the association with these regions of star
formation cannot be ruled out in these cases. In contrast, X26 and X29 in
Messier 101 have radio counterpart candidates with apparently double morphology
(see again Fig. 8). They are located in the peripheral region of the galaxy, so
we could also be dealing with background sources as in the first ULX case
discussed in this section. In particular, X29 reminds of a Fanaroff-Riley Type
II radio galaxy. On the other hand, X26 seems to overlap with a fuzzy optical
object (NGC 5471B) that has been proposed by Jenkins et al. (2004) to be either
an hypernova remnant (HNR) or a supersoft source (SSS) of X-ray binary type.

5. 2005MNRAS.360.1201H
Re:NGC 5457
NGC 5457. M101 is a large nearby galaxy. Observations of CO data (BIMA song;
Helfer et al. 2003) show that the molecular gas is only distributed along the
bar. In the H{alpha} image the gas is distributed over the whole field. Two
large arms can be seen.

6. 2005ApJS..157...59L
Re:NGC 5457
NGC 5457 (M101) is a face-on prototype Sc spiral galaxy at a distance of^6.855
Mpc. ULX1 is coincident with an object with B = 17.80 mag and R = 15.00 mag and
showed variability within a 2 day observation. ULX2 and ULX3 (IXO 83) are both
on spiral arms, both showed variability within a 26 day observation, and the
luminosities of both varied by more than 50% during the four observations in 5

7. 2005A&A...437..837D
Figures 1 and 2 show the variation in the observational emission-line ratios of
the compiled data for M 101 with galactocentric distance Rand our model results.
An angular scale of 1" = 2.25 kpc (Kennicutt & Garnett 1996) was assumed. A
linear behavior of T_eff_ with R was found, which can be represented by
T_eff_(10^4^ K) = (0.037 +/- 0.002) R (kpc) + (3.77 +/- 0.03). No systematic
variation of the ionization parameter along the disk was found, and we obtained
a mean value of log U = -2.54 +/- 0.04, in agreement with Kennicutt & Garnett
(1996), who used the correlation of U with the [S II]/[S III] line ratio
suggested by Diaz et al. (1991). However, Henry & Howard (1995) and Evans
(1986), using photoionization models, concluded that M 101 presents a U
gradient, although their gradients are slightly inconsistent, possibly due to
differences in the stellar atmosphere chosen in their models.
In Fig. 3 we show our gradients for O/H, N/O, and S/O and the abundances
derived from direct electron temperature measurements for individual H II
regions found in the literature (Kennicutt et al. 2003; Rayo et al. 1982;
Torres-Peimbert et al. 1989; van Zee et al. 1998). Also shown in this figure are
the model results of Evans (1986), who built individual photoionization models
in order to reproduce the observations of the H II regions H 40, NGC 5461, and
NGC 5471, and the O/H gradient calculated via P-method and via R_23_ index by
Pilyugin (2001b) using the Edmunds & Pagel (1984) calibration. The N/O gradient
via P-method derived by Pilyugin et al. (2004) is also shown in Fig. 3.
A linear regression in the our oxygen estimates yields 12+log (O/H) = (-0.035
+/- 0.002) R (kpc) + (9.15 +/- 0.04), consistent with the oxygen estimations
obtained by Evans (1986). Our oxygen gradient yields a value of 12+log (O/H) =
8.88 for the H 335 (Searle 5) nebula, similar to the one derived by Kinkel &
Rosa (1994). However, our O/H abundances are larger than those obtained via
direct measurements (e.g. the ones by Kennicutt et al. 2003) by a factor of
0.1-0.3 dex. As can be seen in Fig. 3, the gradient obtained via the P-method
represents the variation of the direct abundances along the M 101 disk very
well, and it is shallower than the other gradients. Similar agreement between
the P-method and direct abundance estimates have also been found recently by
Cedres et al. (2004) and by Kennicutt et al. (2003) in M 101. The gradient
derived via R23 is quite similar to our gradient.
Our inferred results for the N/O ratio match the ones obtained from both
direct measurements and the P-method, and they were fitted by log (N/O) =
(-0.024+/- 0.004) R (kpc) - (0.73 +/- 0.06). The N/O values found by Evans
(1986) are about 0.1 dex lower than ours.
Our predictions marginally suggest an S/O gradient represented by log (S/O) =
(-0.005 +/- 0.003) R (kpc) - (1.53 +/- 0.05). However, as can be noted in Fig.
1, our models failed to match the observed [S II]/[S III] line ratios at high
metallicities, which makes the S/O ratio derived by us for this region very

8. 2004ApJ...608...42S
Re:NGC 5457
NGC 5457 inner. An inner field in M101 was studied by Stetson et al.
(1998) as part of the HST Key Project on the Extragalactic Distance
Scale. In this paper a distance is calculated using a total of 61 bona
fide, high-quality Cepheids, for which Table 4 of Stetson et al. (1998)
lists a quality index larger than 2 under either "Image Quality" or
"Light Curve Quality."

9. 2004ApJ...608...42S
Re:NGC 5457
NGC 5457 outer. HST data were obtained as part of the HST Key Project on
the Extragalactic Distance Scale (Kelson et al. 1996). The distance
calculated in this paper makes use of all 29 Cepheids from the original

10. 2002ApJ...573..306E
Re:NGC 5457
NGC 5457 (M101), South
A map of the (southern) region surrounding NGC 5455 and containing
many of the sources can be seen in Figure 8. SN 1970G is visible as a
prominence pointing to the northwest from {alpha}. Source {alpha} has
a flat spectral index and an excellent positional coincidence with
NGC 5455, a known H II region. Sources {delta} and {omega} have
spectral indexes between 0.0 and 0.1, indicating that they are
likely H II regions as well. If we compare the positions of our
sources with those of H II regions found by Hodge et al. (1990),
we find positional coincidences (within the uncertainties) for
{psi}, {rho}, {theta}, {epsilon}, and {delta}. These are also
probable H II regions. Comparison of the positions of SNRs in
M101 reported by Matonick & Fesen (1997) with our sources reveals
no positional coincidences.

11. 2002ApJ...573..306E
Re:NGC 5457
NGC 5457 (M101), East
A map of the eastern region of M101 (containing the site of SN 1951H)
can be seen in Figure 9. Prominent features include emission regions
from the H II regions NGC 5461 and 5462. Superposition of the radio
map with H{alpha} maps found in Israel, Goss, & Allen (1975) reveals
that sources {kappa}, {eta},{phi}, and {chi} in NGC 5461 lie over
H{alpha} emission regions. The same positional coincidence is found
for and {gamma}, {epsilon}, {delta}, {beta}, and {alpha} in NGC 5462.
All of these are probable H II regions. The positions of our sources
can be compared to H II regions observed by Hodge et al. (1990). We
find that {pi}, {eta}, {phi}, {gamma}, {epsilon}, and {alpha} have
peak positions that are within the uncertainties for the H II regions.
In addition {lambda}, {kappa}, {chi}, {delta}, {beta}, and {theta}
have peak positions within twice the uncertainties of a particular H II
region. The Hodge et al. (1990) data indicate that these sources may
be H II regions.
Both comparisons indicate that {kappa}, {eta}, {phi}, {chi}, {pi},
{gamma}, {epsilon}, {delta}, {beta}, and {alpha} are all probable H II
Comparison with SNRs in M101 from Matonick & Fesen (1997) shows no
SNRs coincident with positions of any of our sources in the eastern
region of M101.

12. 2002AJ....124.2581S
Re:NGC 5457
NGC 5457 (Fig. 4): The bar in NGC 5457 is oriented at
a P.A. of 80^deg^. The molecular gas is primarily on
the leading side of the stellar bar with P.A. ~95^deg^.
The H{alpha} emission tends to be toward the leading
side of the CO emission.
In both halves of the bar the CO intensity
decreases outward from the central concentration of gas,
to the east toward C1 and to the west toward C6. In the
western half of the bar there is one bright CO complex,
labeled "C2" in Figure 4. Generally coincident with but
offset slightly toward the leading side of C2 is a
bright H II region, labeled "H1." Diffuse H{alpha}
emission connecting the nuclear region and H1 is seen
mostly on the leading side of the CO emission in the
region in between C1 and C2. To the south of C2, on the
trailing side, there is a 10" spurlike CO feature,
labeled "C3."
In the eastern half the CO morphology is very
similar to that seen in the western half. C7 is a weak
CO peak ~30" east of the circumnuclear region. Associated
with C7 is weak H{alpha} emission, labeled "H3."
Generally the H{alpha} emission in this half of the bar
is characterized by a continuous ridge extending from
the circumnuclear emission to H4 on the leading side of
the CO. H4, like H2, is on the leading side of the bar
and is probably the beginning of an inner ring.
Toward both bar ends the CO emission deviates away
from the leading side of the bar and connects with the
CO emission in the spiral arms of NGC 5457. The CO region,
labeled "C4," and the H{alpha} region, labeled "H2," are
probably associated with the bar end, but the two bright
CO and H{alpha} peaks 6"-10" north of H2 are associated
with the spiral arm.

13. 2002AJ....124..675C
Re:UGC 08981
M101. The listed S(1.4 GHz) is from Condon (1987).

14. 2002A&A...389...68G
Re:NGC 5457
NGC 5457 (M 101): this galaxy is nearly face-on. Thus, the
values of the PA are not well constrained. Our methods prefer
a galaxy completely face on but, as the galaxy is quite
asymmetrical, we have decided to adopt the values obtained by
the HI high resolution study of Bosma et al. (1981).

15. 2000MNRAS.319...17L
Re:NGC 5457
NGC 5457 (M 101): Observations of this galaxy with the Einstein IPC and
ROSAT PSPC have been widely reported (Trinchieri, Fabbiano & Romaine 1990;
Snowden & Pietsch 1995; Williams & Chu 1995). Results from an ultradeep
(229-ks) ROSAT HRI observation have become available recently (Wang,
Immler & Pietsch 1999). The data reported here were the result of combining
two of the four images used to produce the ultradeep observation reported
by Wang, Immler & Pietsch (1999).
Wang et al. (1999) find a total of 51 point sources down to fluxes
~6 x 10^-15^ erg s^-1^ cm^-2^, of which about half are thought to be
associated with the galaxy. The X-ray emission beautifully traces the
spiral arms of the galaxy and five of the individual sources are associated
with giant H II regions (Williams & Chu 1995), but they are located outside
the ~6 x 6 arcmin^2^ optical JKT image shown in Fig. 27.
From IPC data Trinchieri et al. (1990) find a nuclear X-ray flux of
3 x 10^-13^ erg s^-1^ cm^-2^ within a circle of 90-arcsec radius for the
Einstein (0.2-4.0 keV) bandpass. From the ROSAT HRI observations a nuclear
flux of 4 x 10^-14^ erg s^-1^ cm^-2^ is obtained, an order of magnitude
fainter than the IPC flux. The difference can be explained if sources X2
and X3, which are not resolved by the IPC, were contained within the large
aperture used by Trinchieri et al. (1990), or by the effect of luminous and
highly variable XRBs. The ROSAT HRI count rate found by Wang et al. (1999)
for the nuclear source is identical to our value (0.67 count ks^-1^),
although the inferred fluxes disagree by a factor ~1.5, probably because
different spectral models were assumed.
The presence of a soft diffuse component is discussed by Snowden &
Pietsch (1995) and Read et al. (1997). They find conclusive evidence in
ROSAT PSPC observations for extended emission within the inner 7 arcmin of
the galaxy. The radial profile obtained from the ROSAT HRI observations
shown in Fig. 37 suggests some patchiness in the X-ray. The better
signal-to-noise data analysed by Wang et al. (1999) confirm this result.
An astonishing total of 93 SNRs have been identified in the galaxy
(Matonick & Fesen 1997). Remnants 57 and 54 are consistent with the
positions of sources X2 and X3 seen in Fig. 27. Wang et al. (1999) detected
X-ray emission from two further remnants, but they fall outside our JKT

16. 1999A&AS..136...35S
Re:NGC 5457
NGC 5457 = M 101 -- Rosa & D'Odorico (1986) report of seven surveyed HII
regions with five detections of WR features from the spectra of
D'Odorico et al. (1983). According to the latter, however, only two
regions, Hodge 40 and NGC 5461 (see below), show clear broad
He II {lambda}4686 features; the remaining objects required confirmation
with spectra at higher resolution. Although uncertain, broad
He II {lambda}4686 emission in Hodge 40 was also pointed out by Rayo
et al. (1982).

17. 1997AstL...23..656G
M 101. Sandage (1983) (photographic photometry). The LF and V(5) may actually
differ markedly from those used here.

18. 1997AstL...23..644G
M 101. Alves and Cook (1995); (Cepheids) Humphreys et at. (1986) (HS58, R7,
HS57); Humphreys and Aaronson (1987a, 1987b) (B162, B189, IVb85). The distance
modulus was corrected in accordance with the assumed distance modulus for the
LMC. The magnitudes and colors of the stars were determined by Sandage (1983).

19. 1997AJ....114.2428S
Re:NGC 5457
NGC 5457 (M101): This is a nearly face-on Sc galaxy with i~18^deg^. CO emission
has been detected near the systemic velocity (241 km s^-1^), with a velocity
width of ~70 km s^-1^, which corresponds to 230 km s^-1^ within the disk plane.
The northern half shows stronger emission with a negative velocity, while the
southern half is not clearly detected. However, if two weak emission peaks in
the north at v_hel_~170 km s^-1^ and in the south at V_hel_~350 km s^-1^ are
due to the rotation, the rotation velocity is estimated to be as high as ~290
km s^-1^ within the central ~10" (350 pc). For the poor data and low
inclination, no rotation curve has been obtained.

20. 1994CAG1..B...0000S
Re:NGC 5457
Hubble Atlas, pp. 27, 31
June 9/10, 1950
30 min
M101, like NGC 1232 two panels back, is
the prototype of the multiple-armed Sc class,
luminosity class I, subtype (s), where the arms
begin at the center rather than from an internal
ring. The two main arms at the center branch
into multiple fragments outward. Thin, intricate
dust lanes are closely associated with the
luminous fragments. The entire face of the galaxy
is well resolved into individual brightest stars
and HII regions.
M101, the closest ScI galaxy to us, has been
important in the steps toward a correct calibration
of the extragalactic distance scale.
Hubble's (1936a) distance modulus for
M101 was small, at m - M = 24.0. The modulus
was increased in the Hubble Atlas to m - M = 27.0
(D = 2.5 Mpc). It is now known that even
this value is 2.3 magnitudes too small. Following
work on the distance scale in the early 1970's
when Cepheid variables could not be found with
the 200-inch telescope (Sandage and Tammann
1974c), the modulus was increased to m - M = 29.3,
which is 5.3 magnitudes farther than
Hubble's 1936 value.
This large increase provided the third step
upward in the revision of Hubble's distance
scale. The first was Baade's increased distance to
M31 in 1952. The second was the increased
distance to NGC 2403 (Tammann and Sandage
1968) based on the identification and measurement
of Cepheids beyond the Local Group.
The 1974 photometry of the stellar content
of M101 was extended in the 1980's (Sandage
1983 b). Brightest blue stars, of which some are
bright irregular supergiant variables, begin to
resolve at magnitude V = 18.9. The brightest red
supergiants resolve beginning at V = 20.3.
M101 is at the center of a group of highly
resolved dwarf galaxies all with small redshift.
The companions include NGC 5204, 5474,
5477, 5585, and Ho IV. A discussion of the
group and photographs of the companions are
given elsewhere (Sandage and Tammann 1974c).
The mean redshift of the group is = 402 km/s.
The redshift of M101 itself is v_o = 372 km/s.
The angular diameter of M101 to an
isophote of 25 mag arc sec^2^ is large at 27'. A
pictorial comparison of the angular diameters of
the giant ScI galaxies M101, M51, NGC 628,
NGC 5248, and the three largest spirals in the
Virgo Cluster (NGC 4254, 4303, and 4321) is
given elsewhere (Sandage and Tammann 1976b),
where it is shown that the angular sizes scale well
as the inverse of the measured redshifts. This is
one of several independent ways to demonstrate
that there is very little noise in the local Hubble
linear expansion velocity flow.

21. 1993ApJS...86....5K
Re:NGC 5457
NGC 5457 (M101); Sc, H II.
This face-on nearby Sc galaxy has a large angular size (~30') and is the
most luminous member of a rich group. NGC 5457 is tidally interacting
with NGC 5474, NGC 5477, and Ho IV, resulting in a distortion of the H I
distribution in its outer regions (Davies, Davidson, & Johnson 1980). The
most striking X-ray features for this galaxy are in the disk, where
several bright and distinct pointlike sources are found, while the
nucleus shows only extended and not particularly strong emission. The
disk sources are likely to be individual massive binary systems
associated with H II regions and OB associations (Trinchieri, Fabbiano, &
Romaine 1990). M 101 is dominated in the UV by extreme Population I in
the form of OB complexes (Hill, Bohlin, & Stecher 1984), which spread
from its nucleus to the spiral arms, and of which 1264 have been
identified (Hodge et al. 1990). The IUE spectrum shows a slowly rising
blue continuum with deep absorption features, indicating star formation
activity and a mixed stellar population from type O(C IV and Si IV
absorption lines) through B (C IV, Si IV, and the lines for {lambda} <
1350 A) to mid-A (features for {lambda} > 1750A).

22. 1976RC2...C...0000d
Re:NGC 5457
= M101
= Arp 026
= VV 344
= 4C 54.30.1
Details (HII regions) = NGC 5447, NGC 5453, NGC 5455, NGC 5461, NGC 5462,
and NGC 5471.
IAU Symp. No.38, 28, 1970.
Astr. Ap., 29, 57, 1973.
Astr. Ap., 29, 447, 1973.
Ap. J., 194, 223, 1974.
IAU Symp. No.38, 13, 1970.
"Supernovae & SN Remnants", Ap. & Space Sc. Lib., 45, 52, 1974.
Photometry (UBV):
Astr. Ap., 5, 413, 1970.
M.N.R.A.S., 162, 359, 1973.
Photometry (I.R. 1-10 microns):
Ap. J. (Letters), 176, L95, 1972.
M.N.R.A.S., 162, 359, 1973.
Photometry (Brightest stars and Variable stars):
Ap. J., 194, 223, 1974.
Astr. Ap., 9, 181, 1970.
Observatory, 88, 239, 1968.
Sov. A.J., 13, 593, 1970.
Sov. A.J., 16, 628, 1973.
Spectrophotometry (far UV):
N.A.S.A., SP 310, 559, 1972.
P.A.S.P., 79, 600, 1967 (in emission region).
Rotation Curve and Mass Determination:
Astrophys. Lett., 8, 17, 1971.
HII Regions:
"Atlas and Catalogue", Univ. Washington, Seattle, 1966.
Ap. J., 155, 417, 1969.
Ap. J., 194, 223, 1974.
HII Regions (I.R. 10-20 micron upper limits):
Ap. J. (Letters), 193, L7, 1974.
HII Regions (Spectrophotometry):
Ap. J., 159, 809, 1970.
Ap. J., 161, 33, 1970.
Ap. J., 168, 327, 1971.
Bull. A.A.S., 5, 448, 1973.
HII Regions (Distance Modulus):
Ap. J., 194, 223, 1974.
Interferometry H{alpha}:
Astr. Ap., 9, 181, 1970.
Astr. Ap., 12, 379, 1971.
Ap. J., 194, 223, 1974.
"Supernovae & SN Remnants", Ap. & Space Sc. Lib., 45, 215, 1974.
Ap. J., 194, 223, 1974.
IAU Circ. No. 2269, 1970.
IAU Circ. No. 2271, 1970.
IAU Circ. No. 2282, 1970.
IAU Circ. No. 2292, 1970.
Yamamoto Circ. No. 1725, 1970.
Info. Bull. Var. Stars, No. 505, 1971.
Ast. Tsirk., No. 679, 1972.
Sov. A.J., 16, 7, 1972.
Ap. J., 174, 383, 1972.
Ap. J., 185, 303, 1973.
Ap. J., 193, 27, 1974.
Astr. Ap., 29, 57, 1973.
Nature, Phys. Sc., 243, 42, 1973.
J.R.A.S. Canada, 68, 36, 1974.
"Supernovae & SN Remnants", Ap. & Space Sc. Lib., Vol. 45, 145, 1974.
Highlights of Ast., 3, 533, 1974.
HI 21cm:
Ap. J., 150, 8, 1967.
Ap. J., 176, 315, 1972.
Nature, 221, 531, 1969.
Astr. Ap., 7, 141, 1970.
Astr. Ap., 12, 108, 1971.
Astr. Ap., 13, 99, 1971.
Astr. Ap., 13, 108, 1971.
Astr. Ap., 29, 447, 1973.
IAU Symp. No.44, 12, 1972.
IAU Symp. No.58, 427, 1974.
Proc. 1st European Astr. Meeting, Vol. 3, 15, 1974.
Radio Observations:
Ap. J., 142, 1333, 1965.
Ap. J., 176, 315, 1972.
A.J., 78, 18, 1973.

23. 1973UGC...C...0000N
Re:UGC 08981
VV 344a, Arp 26
SAB(rs)cd (de Vaucouleurs), Sc- (Holmberg)
NGC 5447, NGC 5449, NGC 5450, NGC 5451, NGC 5453, NGC 5455, NGC 5458, NGC 5461,
NGC 5462, and NGC 5471 are condensations in this galaxy
SN 1909
In Arp's class "spiral galaxies with one heavy arm"
"Note straight arm, bright knot on east appears almost stellar" (Arp)

24. 1964RC1...C...0000d
Re:NGC 5457
= M101
NGC 5447, NGC 5453, NGC 5455, NGC 5458, NGC 5461, NGC 5462, and NGC 5471 are
HII regions.
Lick 13 dimensions are for the bright part only.
Ritchey, L'Evolution de l'Astrophotographie..., S.A.F., Paris 1929.
Ap. J., 50, 385, 1919.
Ap. J., 83, 424, 1936.
Ap. J., 91, 528, 1940.
Ap. J., 108, 415, 1948.
Medd. Lund II, 128, 1950.
Sov. A.J. 32, 16, 1955.
Izv. Pulkovo, 20, No.156, 87, 1956.
Pubbl. Byurakan, XXIV, 2, 1958.
Error on V magnitude in Ap. J. Suppl., No. 48, 1961, V = 12.36 for A/D(0)
= 0.025
HII Regions:
Ap. J., 91, 261, 1940.
Observatory, 79, 54, 1959.
Zeit. fur Ap., 50, 168, 1960.
Radio Emission:
Handbuch d. Phys., 53, 253, 1959.
P.A.S.P., 72, 368, 1960.
M.N.R.A.S., 122, 479, 1961.
HI Emission:
B.A.N., 14, 323, 1959.
A.J., 67, 317, 1962.
SN 1908/9
A.N., 180, 375, 1909.
Ap. J., 69, 27, 1929.
Ap. J., 88, 293, 1938.

25. 1961Hubbl.B...0000S
Re:NGC 5457
Messier 101
July 17/18, 1950
30 min
Enlarged 2.6X
M101 is the prototype of the multiple-arm galaxies of the
Sc section. Although many separate arms exist in the
outer regions, each one can be traced from a branching of
two principal dust arms which begin in the nucleus. This
dust pattern is shown in the illustration of the central
region on page 31. As in M51, many dust arms exist in
the central lens. They cannot be traced as individual arms
but rather as separate segments which, when taken together,
form a rough spiral pattern. The entire spiral
pattern over the face of M51 is dominated by the dust
lanes, which usually are on the inside of the bright
luminous spiral filaments. The outer segments of the
luminous arms are thoroughly resolved into individual stars
and a few HII regions. The outer arms are highly
branched. The surface brightness of the arms in the
northwest quadrant of the spiral is very low, and the
resolved stars in these arms are faint. The brightest arms
are in the southwest quadrant. Notice the resolved clumps
or associations of stars in the brightest arm on the east
side. The most conspicuous of the associations is elliptical,
with a major and minor axis of 50 sec and 15 sec of
arc, respectively. The distance modulus of M101 is about
27.0, which makes the linear dimensions of the association
about 620 parsecs by 190 parsecs. The average width of
an arm is about 30 sec of arc, corresponding to 380 parsecs.
The largest HII regions are about 10 sec of arc in
diameter, which corresponds to 120 parsecs. This is
smaller by about a factor of 6 than the 30 Doradus complex
in the Large Magellanic Cloud and smaller by about
a factor of 3 than NGC 0604 in M33. 30 Doradus is about
640 parsecs in diameter; NGC 0604, about 320 parsecs.
Many Sc galaxies are of the M101 type. The characteristics
of the type are (1) a small nucleus from which the
spiral pattern emerges in dust lanes, at first, and farther
out in luminous filaments; (2) multiple spiral arms, thin
and highly branched in their outer regions; (3) arms well
resolved into individual stars and H II regions.
The integrated color indices of Sc galaxies are instructive.
Erik Holmberg has measured magnitudes and colors
for a number of galaxies, and his results have direct bearing
on the classification problem. Spirals like M101, in
which the entire structure is dominated by the spiral
arms, have blue colors. M101 itself has an international
color index of 0.30. Most of the galaxies on page 29 have
colors in the range 0.30 to 0.50. The more open, chaotic
spirals like M101 or NGC 0628 (pg. 29) are bluer than spirals
like NGC 4321 (M100, pg. 28).

26. 1961Hubbl.B...0000S
Re:NGC 5457
Messier 101
May 10/11, 1950
40 min
Enlarged 12.1X
The nucleus of M101 is similar to that of M100 (above).
Two principal dust lanes cut into the very center. It is
the dust rather than the luminous arcs that defines the
spiral pattern in this region. The two central dust patches,
however, unlike those in M100, cannot be traced as single
lanes into the outer regions. The entire inner lens of M101
is crossed by segments of dust arms. Although the segments,
taken as a whole, define a spiral pattern, they cannot
be connected with one another to form continuous lanes.
The entire face of M101 is shown on page 37.

27. 1959VV....C...0000V
Re:VV 344a
= NGC 5457
= Messier 101
V = +394 km/sec
Yerkes Type: fS1

28. 1918PLicO..13....9C
Re:NGC 5457
Vol. VIII, Plate 49. M.101. This unusually beautiful spiral is about 16' in
diameter. There is an almost stellar nucleus, with two bright condensations
very. close which give it a tri-nuclear appearance. The open whorls show
a multitude of stellar condensations. 5449, 5450, 5451, 5453, 5455, 5458,
5461, 5462, are simply brighter knots in the great nebula. 10 s.n.

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