38 research outputs found
Tropospheric sounding with low-cost particulate matter sensors
The high-altitude balloon (HAB) platform has allowed scientists to measure vertical profiles in the atmosphere at a relatively low cost. The current project combines the HAB platform with low-cost air quality sensors that measure particulate matter (PM). PM is detrimental to human health and can exacerbate asthma. In the atmosphere, PM can affect cloud formation and also radiative transfer, which links emissions of PM to climate change. Therefore, understanding and controlling PM emissions is vital to air quality and climate change. In agricultural regions, several practices produce significant PM emissions. Tilling can release PM in the form of dust, especially under arid conditions. The burning of crop residue is also a common practice practice that releases PM in the form of partially combusted organics (soot). The ultimate goal of this project is to use low-cost PM sensors and HAB to assess PM sources from agricultural regions using citizen scientists. The current presentation evaluates the performance of two different PM sensors over flights conducted during the summer of 2017
A Morphological and Multicolor Survey for Faint QSOs in the Groth-Westphal Strip
Quasars representative of the populous faint end of the luminosity function
are frustratingly dim with m~24 at intermediate redshift; moreover groundbased
surveys for such faint QSOs suffer substantial morphological contamination by
compact galaxies having similar colors. In order to establish a more reliable
ultrafaint QSO sample, we used the APO 3.5-m telescope to take deep groundbased
U-band CCD images in fields previously imaged in V,I with WFPC2/HST. Our
approach hence combines multicolor photometry with the 0.1" spatial resolution
of HST, to establish a morphological and multicolor survey for QSOs extending
about 2 magnitudes fainter than most extant groundbased surveys. We present
results for the "Groth-Westphal Strip", in which we identify 10 high likelihood
UV-excess candidates having stellar or stellar-nucleus+galaxy morphology in
WFPC2. For m(606)<24.0 (roughly B<24.5) the surface density of such QSO
candidates is 420 (+180,-130) per square degree, or a surface density of 290
(+160,-110) per square degree with an additional V-I cut that may further
exclude compact emission line galaxies. Even pending confirming spectroscopy,
the observed surface density of QSO candidates is already low enough to yield
interesting comparisons: our measures agree extremely well with the predictions
of several recent luminosity function models.Comment: 29 pages including 6 tables and 7 figures. As accepted for
publication in The Astronomical Journal (minor revisions
Cataclysmic Variables and Other Compact Binaries in the Globular Cluster NGC 362: Candidates from Chandra and HST
Highly sensitive and precise X-ray imaging from Chandra, combined with the
superb spatial resolution of HST optical images, dramatically enhances our
empirical understanding of compact binaries such as cataclysmic variables and
low mass X-ray binaries, their progeny, and other stellar X-ray source
populations deep into the cores of globular clusters. Our Chandra X-ray images
of the globular cluster NGC 362 reveal 100 X-ray sources, the bulk of which are
likely cluster members. Using HST color-magnitude and color-color diagrams, we
quantitatively consider the optical content of the NGC 362 Chandra X-ray error
circles, especially to assess and identify the compact binary population in
this condensed-core globular cluster. Despite residual significant crowding in
both X-rays and optical, we identify an excess population of H{\alpha}-emitting
objects that is statistically associated with the Chandra X-ray sources. The
X-ray and optical characteristics suggest that these are mainly cataclysmic
variables, but we also identify a candidate quiescent low mass X-ray binary. A
potentially interesting and largely unanticipated use of observations such as
these may be to help constrain the macroscopic dynamic state of globular
clusters.Comment: 6 pages, 6 figures, to appear in the proceedings of the conference
"Binary Star Evolution: Mass Loss, Accretion, and Mergers," Mykonos, Greece,
June 22-25, 201
Tracing kinematical and physical asymmetries in the jet from DG Tau B
Stellar jets can be highly asymmetric and have multiple velocity components.
To clarify the origin of jet asymmetries and constrain their launch mechanism
we study the physical and kinematical structure of the flow emitted by DG Tau
B. The analysis of deep spectra taken at the KECK telescope allows us to infer
the physical properties (the electron and total density, ne and nh, the
ionisation fraction, xe, and the temperature, te) and the spatial distribution
of the velocity components in the two jet lobes. The presence of dust grains in
the jet is investigated by estimating the gas-phase abundance of calcium with
respect to its solar value. At the base of the jet the lines are broad (~100
km/s) and up to three velocity components are detected. At 5" from the source,
however, only the denser and more excited high velocity components survive and
the lines are narrower (~10-30 km/s). The jet is strongly asymmetric both in
velocity and in its physical structure. The red lobe, slower (~140 km/s) and
more collimated, presents low ionisation fractions (xe~0.1-0.4) and
temperatures (te<5e3 K), while the total density is up to ~2.5e4 ccm. The blue
lobe, faster (~-320 km/s) and less collimated, is also less dense (nh~1e4 ccm)
but highly excited (te up to ~5e4 K and xe up to 0.9). The estimated mass loss
rate is similar in the two lobes (~6-8e-9 Msol/yr), suggesting that the
ejection power is comparable on the two sides of the system, as expected from a
magneto-centrifugal ejection mechanism, and that the observed asymmetries are
due to different mass load and propagation properties in an inhomogeneous
environment. Calcium is strongly depleted, indicating that the jet contains
dust grains and, therefore, should originate from a region of the disk
extending beyond the dust sublimation radius. The depletion is lower for higher
velocities, consistent with dust destruction by shocks.Comment: 14 pages, 9 figures, accepted by A&
A combined optical/infrared spectral diagnostic analysis of the HH1 jet
Complete flux-calibrated spectra covering the spectral range from 6000 A to
2.5 um have been obtained along the HH1 jet and analysed in order to explore
the potential of a combined optical/near-IR diagnostic applied to jets from
young stellar objects. Important physical parameters have been derived along
the jet using various diagnostic line ratios. This multi-line analysis shows,
in each spatially unresolved knot, the presence of zones at different
excitation conditions, as expected from the cooling layers behind a shock
front. In particular, a density stratification in the jet is evident from
ratios of various lines of different critical density. In particular, [FeII]
lines originate in a cooling layer located at larger distances from the shock
front than that generating the optical lines, where the compression is higher
and the temperature is declining. The derived parameters were used to measure
the mass flux along the jet, adopting different procedures, the advantages and
limitations of which are discussed. dM/dt is high in the initial part of the
flow but decreases by about an order of magnitude further out. Conversely, the
mass flux associated with the warm molecular material is low and does not show
appreciable variations along the jet. We suggest that part of the mass flux in
the external regions is not revealed in optical and IR lines because it is
associated with a colder atomic component, which may be traced by the far-IR [O
I]63 um line.
Finally, we find that the gas-phase abundance of refractory species is lower
than the solar value suggesting that a significant fraction of dust grains may
still be present in the jet beam.Comment: Accepted on Astronomy & Astrophysic
Recipes for stellar jets: results of combined optical/infrared diagnostics
We examine the conditions of the plasma along a sample of 'classical'
Herbig-Haro jets located in the Orion and Vela star forming regions, through
combined optical-infrared spectral diagnostics. Our sample includes HH 111, HH
34, HH 83, HH 73, HH 24 C/E, HH 24 J, observed at moderate spatial/spectral
resolution. The obtained spectra cover a wide wavelength range from 0.6-2.5 um,
including many transitions from regions of different excitation conditions.
This allows us to probe the density and temperature stratification which
characterises the cooling zones behind the shock fronts along the jet. The
derived physical parameters (such as the extinction, the electron density and
temperature, the ionisation fraction, and the total density) are used to
estimate the depletion onto dust grains of Calcium and Iron with respect to
solar abundances. This turns out to be between 70% and 0% for Ca and ~90% for
Fe, suggesting that the weak shocks present in the beams are not capable of
completely destroying the dust grains. We then derive the mass flux rates
(Mdot_jet is on average 5 10^-8 M_solar yr^-1) and the associated linear
momentum fluxes. The latter are higher than, or of the same order as, those
measured in the coaxial molecular flows, suggesting that the flows are jet
driven. Finally, we discuss differences between jets in our sample.Comment: 19 pages, 15 figures, accepted by A&
Sub-arcsecond [FeII] spectro-imaging of the DG Tau jet: Periodic bubbles and a dusty disk wind?
We present SINFONI/VLT observations of the DG Tauri jet in the [FeII] lines
with 0.15" angular resolution and R=3000 spectral resolution. We observe an
onion-like velocity structure in [FeII] in the blueshifted jet, similar to that
observed in optical lines. High-velocity gas at ~-200 km/s is collimated inside
a half-opening angle of 4 degrees and medium-velocity gas at ~-100 km/s in a
cone with an half-opening angle 14 degrees. Two new axial jet knots are
detected in the blue jet, as well as a more distant bubble with corresponding
counter-bubble. The periodic knot ejection timescale is revised downward to 2.5
yrs. The redshifted jet is detected only beyond 0.7" from the star, yielding
revised constraints on the disk surface density. From comparison to [OI] data
we infer iron depletion of a factor 3 at high velocities and a factor 10 at
speeds below -100 km/s. The mass-fluxes in each of the medium and high-velocity
components of the blueshifted lobe are ~1.6+-0.8x10^-8 Msun/yr, representing
0.02-0.2 of the disk accretion rate. The medium-velocity conical [FeII] flow in
the DG Tau jet is too fast and too narrow to trace photo-evaporated matter from
the disk atmosphere. Both its kinematics and collimation cannot be reproduced
by the X-wind, nor can the "conical magnetospheric wind". The level of Fe gas
phase depletion in the DG Tau medium-velocity component also rules out a
stellar wind and a cocoon ejected sideways from the high-velocity beam. A
quasi-steady centrifugal MHD disk wind ejected over 0.25-1.5 AU and/or episodic
magnetic tower cavities launched from the disk appear as the most plausible
origins for the medium velocity component in the DG Tau jet. The same disk wind
model can also account for the properties of the high-velocity flow, although
alternative origins in magnetospheric and/or stellar winds cannot be excluded
for this component
Properties of the ionized gas in HH202. II: Results from echelle spectrophotometry with UVES
We present results of deep echelle spectrophotometry of the brightest knot of
the HH202 in the Orion Nebula --HH202-S-- using the ultraviolet Visual Echelle
Spectrograph (UVES). The high spectral resolution has permitted to separate the
component associated with the ambient gas from that associated with the gas
flow. We derive electron densities and temperatures for both components, as
well as the chemical abundances of several ions and elements from collisionally
excited lines, including the first determinations of Ca^{+} and Cr^{+}
abundances in the Orion Nebula. We also calculate the He^{+}, C^{2+}, O^{+} and
O^{2+} abundances from recombination lines. The difference between the O^{2+}
abundances determined from collisionally excited and recombination lines --the
so-called abundance discrepancy factor-- is 0.35 dex and 0.11 dex for the shock
and nebular components, respectively. Assuming that the abundance discrepancy
is produced by spatial variations in the electron temperature, we derive values
of the temperature fluctuation parameter, t^2, of 0.050 and 0.016, for the
shock and nebular components, respectively. Interestingly, we obtain almost
coincident t^2 values for both components from the analysis of the intensity
ratios of He I lines. We find significant departures from case B predictions in
the Balmer and Paschen flux ratios of lines of high principal quantum number n.
We analyze the ionization structure of HH202-S, finding enough evidence to
conclude that the flow of HH202-S has compressed the ambient gas inside the
nebula trapping the ionization front. We measure a strong increase of the total
abundances of nickel and iron in the shock component, the abundance pattern and
the results of photoionization models for both components are consistent with
the partial destruction of dust after the passage of the shock wave in HH202-S.Comment: 23 pages, 7 figures. Accepted for publication in MNRA
Iron abundance in HII regions
Optical CCD spectra are used to determine the Fe abundances at several
positions inside seven bright Galactic HII regions. The observed [FeIII] line
ratios are compared with the predictions of different sets of collision
strengths and transition probabilities for this ion to select the atomic data
providing the best fit to the observations. The values found for the Fe++ and
Fe+ abundances, along with ionization correction factors for the contribution
of Fe3+, obtained from available grids of photoionized models, imply that the
Fe/O ratio in the ionized gas is between 2% and 30% of solar. The Fe abundances
derived for each area are correlated both with the degree of ionization and the
colour excess. A possible explanation is suggested, namely the presence of a
population of small grains, probably originating from the fragmentation of
larger grains. These small grains would release Fe atoms into the gas after the
absorption of energetic photons; the small grains surviving this destruction
process would be swept out of the ionized region by the action of radiation
pressure or stellar winds. An indication of a further and more efficient
destruction agent is given by the high Fe abundance derived for a position
sampling the optical jet H399 in M20, where dust destruction due to shock waves
has presumably taken place.Comment: A&A, accepted for publication, 12 page