68 research outputs found
The Nearby and Extremely Metal-Poor Galaxy CGCG 269-049
We present Hubble Space Telescope (HST) and Spitzer Space Telescope images
and photometry of the extremely metal-poor (Z = 0.03 Z_sol) blue dwarf galaxy
CGCG 269-049. The HST images reveal a large population of red giant and
asymptotic giant branch stars, ruling out the possibility that the galaxy has
recently formed. From the magnitude of the tip of the red giant branch, we
measure a distance to CGCG 269-049 of only 4.9 +/- 0.4 Mpc. The spectral energy
distribution of the galaxy between ~3.6 - 70 microns is also best fitted by
emission from predominantly ~10 Gyr old stars, with a component of thermal dust
emission having a temperature of 52 +/- 10 K. The HST and Spitzer photometry
indicate that more than 60% of CGCG 269-049's stellar mass consists of stars
~10 Gyr old, similar to other local blue dwarf galaxies. Our HST H-alpha image
shows no evidence of a supernova-driven outflow that could be removing metals
from the galaxy, nor do we find evidence that such outflows occurred in the
past. Taken together with CGCG 269-049's large ratio of neutral hydrogen mass
to stellar mass (~10), these results are consistent with recent simulations in
which the metal deficiency of local dwarf galaxies results mainly from
inefficient star formation, rather than youth or the escape of supernova
ejecta.Comment: 35 Pages, 7 Figures, accepted for publication in ApJ; new version
corrects errors in Table 1, Figure 3, and related calculations in tex
Wolf 1130: A Nearby Triple System Containing a Cool, Ultramassive White Dwarf
Following the discovery of the T8 subdwarf WISEJ200520.38+542433.9 (Wolf
1130C), with common proper motion to a binary (Wolf 1130AB) consisting of an M
subdwarf and a white dwarf, we set out to learn more about the old binary in
the system. We find that the A and B components of Wolf 1130 are tidally
locked, which is revealed by the coherence of more than a year of V band
photometry phase folded to the derived orbital period of 0.4967 days. Forty new
high-resolution, near-infrared spectra obtained with the Immersion Grating
Infrared Spectrometer (IGRINS) provide radial velocities and a projected
rotational velocity (v sin i) of 14.7 +/- 0.7 km/s for the M subdwarf. In
tandem with a Gaia parallax-derived radius and verified tidal-locking, we
calculate an inclination of i=29 +/- 2 degrees. From the single-lined orbital
solution and the inclination we derive an absolute mass for the unseen primary
(1.24+0.19-0.15 Msun). Its non-detection between 0.2 and 2.5 microns implies
that it is an old (>3.7 Gyr) and cool (Teff<7000K) ONe white dwarf. This is the
first ultramassive white dwarf within 25pc. The evolution of Wolf 1130AB into a
cataclysmic variable is inevitable, making it a potential Type Ia supernova
progenitor. The formation of a triple system with a primary mass >100 times the
tertiary mass and the survival of the system through the common-envelope phase,
where ~80% of the system mass was lost, is remarkable. Our analysis of Wolf
1130 allows us to infer its formation and evolutionary history, which has
unique implications for understanding low-mass star and brown dwarf formation
around intermediate mass stars.Comment: 37 pages, 9 Figures, 5 Table
The Chemical Compositions of Very Metal-Poor Stars HD 122563 and HD 140283; A View From the Infrared
From high resolution (R = 45,000), high signal-to-noise (S/N > 400) spectra
gathered with the Immersion Grating Infrared Spectrograph (IGRINS) in the H and
K photometric bands, we have derived elemental abundances of two bright,
well-known metal-poor halo stars: the red giant HD 122563 and the subgiant HD
140283. Since these stars have metallicities approaching [Fe/H] = -3, their
absorption features are generally very weak. Neutral-species lines of Mg, Si, S
and Ca are detectable, as well as those of the light odd-Z elements Na and Al.
The derived IR-based abundances agree with those obtained from
optical-wavelength spectra. For Mg and Si the abundances from the infrared
transitions are improvements to those derived from shorter wavelength data.
Many useful OH and CO lines can be detected in the IGRINS HD 122563 spectrum,
from which derived O and C abundances are consistent to those obtained from the
traditional [O I] and CH features. IGRINS high resolutions H- and K-band
spectroscopy offers promising ways to determine more reliable abundances for
additional metal-poor stars whose optical features are either not detectable,
or too weak, or are based on lines with analytical difficulties.Comment: Accepted for publication in ApJ (28 pages, 4 tables, 6 figures
High-resolution near-IR Spectral mapping with H and [Fe II] lines of Multiple Outflows around LkH 234
We present a high-resolution, near-IR spectroscopic study of multiple
outflows in the LkH 234 star formation region using the Immersion
GRating INfrared Spectrometer (IGRINS). Spectral mapping over the blueshifted
emission of HH 167 allowed us to distinguish at least three separate, spatially
overlapped, outflows in H and [Fe II] emission. We show that the H
emission represents not a single jet, but complex multiple outflows driven by
three known embedded sources: MM1, VLA 2, and VLA 3. There is a redshifted
H outflow at a low velocity, \VLSR 50 {\kms}, with respect to
the systemic velocity of \VLSR 11.5 {\kms}, that coincides with the
HO masers seen in earlier radio observations two arcseconds southwest of
VLA 2. We found that the previously detected [Fe II] jet with \VLSR
100 {\kms} driven by VLA 3B is also detected in H emission, and confirm
that this jet has a position angle about 240. Spectra of the
redshifted knots at 14\arcsec65\arcsec northeast of LkH 234 are
presented for the first time. These spectra also provide clues to the existence
of multiple outflows. We detected high-velocity (50120 {\kms}) H gas
in the multiple outflows around LkH 234. Since these gases move at
speeds well over the dissociation velocity ( 40 {\kms}), the emission must
originate from the jet itself rather than H gas in the ambient medium.
Also, position-velocity diagrams and excitation diagram indicate that emission
from knot C in HH 167 come from two different phenomena, shocks and
photodissociation.Comment: 32 pages, 12 figures, 2 tables, Accepted for publication in the
Astrophysical Journa
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